It is currently 23 Oct 2017, 14:14

Close

GMAT Club Daily Prep

Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.

Customized
for You

we will pick new questions that match your level based on your Timer History

Track
Your Progress

every week, we’ll send you an estimated GMAT score based on your performance

Practice
Pays

we will pick new questions that match your level based on your Timer History

Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here.

Close

Request Expert Reply

Confirm Cancel

Events & Promotions

Events & Promotions in June
Open Detailed Calendar

D01-13

  new topic post reply Question banks Downloads My Bookmarks Reviews Important topics  
Author Message
TAGS:

Hide Tags

Intern
Intern
avatar
Joined: 07 Dec 2015
Posts: 3

Kudos [?]: 5 [0], given: 25

Location: Nepal
Concentration: Finance, Statistics
GPA: 3
Re D01-13 [#permalink]

Show Tags

New post 17 Mar 2016, 08:21
I think this the explanation isn't clear enough, please elaborate.

Kudos [?]: 5 [0], given: 25

Intern
Intern
avatar
Joined: 07 Dec 2015
Posts: 3

Kudos [?]: 5 [0], given: 25

Location: Nepal
Concentration: Finance, Statistics
GPA: 3
Re D01-13 [#permalink]

Show Tags

New post 17 Mar 2016, 08:24
I think this the explanation isn't clear enough, please elaborate. i dont understand why -2 is not a solution .
for instance squrt of 4 has 2 soln i.e 2 and -2. please explain?

Kudos [?]: 5 [0], given: 25

Expert Post
2 KUDOS received
Math Expert
User avatar
V
Joined: 02 Sep 2009
Posts: 41913

Kudos [?]: 129505 [2], given: 12201

Re: D01-13 [#permalink]

Show Tags

New post 17 Mar 2016, 10:27
2
This post received
KUDOS
Expert's post
1
This post was
BOOKMARKED
sabinadhikari99 wrote:
I think this the explanation isn't clear enough, please elaborate. i dont understand why -2 is not a solution .
for instance squrt of 4 has 2 soln i.e 2 and -2. please explain?


That's not true.

When the GMAT provides the square root sign for an even root, such as \(\sqrt{x}\) or \(\sqrt[4]{x}\), then the only accepted answer is the positive root.

That is, \(\sqrt{25}=5\), NOT +5 or -5. In contrast, the equation \(x^2=25\) has TWO solutions, +5 and -5. Even roots have only a positive value on the GMAT.
_________________

New to the Math Forum?
Please read this: Ultimate GMAT Quantitative Megathread | All You Need for Quant | PLEASE READ AND FOLLOW: 12 Rules for Posting!!!

Resources:
GMAT Math Book | Triangles | Polygons | Coordinate Geometry | Factorials | Circles | Number Theory | Remainders; 8. Overlapping Sets | PDF of Math Book; 10. Remainders | GMAT Prep Software Analysis | SEVEN SAMURAI OF 2012 (BEST DISCUSSIONS) | Tricky questions from previous years.

Collection of Questions:
PS: 1. Tough and Tricky questions; 2. Hard questions; 3. Hard questions part 2; 4. Standard deviation; 5. Tough Problem Solving Questions With Solutions; 6. Probability and Combinations Questions With Solutions; 7 Tough and tricky exponents and roots questions; 8 12 Easy Pieces (or not?); 9 Bakers' Dozen; 10 Algebra set. ,11 Mixed Questions, 12 Fresh Meat

DS: 1. DS tough questions; 2. DS tough questions part 2; 3. DS tough questions part 3; 4. DS Standard deviation; 5. Inequalities; 6. 700+ GMAT Data Sufficiency Questions With Explanations; 7 Tough and tricky exponents and roots questions; 8 The Discreet Charm of the DS; 9 Devil's Dozen!!!; 10 Number Properties set., 11 New DS set.


What are GMAT Club Tests?
Extra-hard Quant Tests with Brilliant Analytics

Kudos [?]: 129505 [2], given: 12201

Intern
Intern
avatar
B
Joined: 11 Jan 2015
Posts: 25

Kudos [?]: 6 [0], given: 11

GMAT ToolKit User
Re: D01-13 [#permalink]

Show Tags

New post 26 Mar 2016, 16:24
Hi Bunuel, would the following be a valid approach to this question or just luck?

1.) Re-arrange and factor out \(x^2: x^2(x^2−x−6)=0\) --> So one solution is 0 -> \(x^2\)
2.) Use discriminant for the left equation \((x^2−x−6)=0\): \(b^2 - 4ac\) --> 1-(4*1*(-6)) -> 25 -> Since 25 is positive the left equation has two solutions
3.) 1.) + 2.) = 3 Solutions

Kudos [?]: 6 [0], given: 11

Expert Post
Math Expert
User avatar
V
Joined: 02 Sep 2009
Posts: 41913

Kudos [?]: 129505 [0], given: 12201

Re: D01-13 [#permalink]

Show Tags

New post 27 Mar 2016, 02:47
paddy41 wrote:
Hi Bunuel, would the following be a valid approach to this question or just luck?

1.) Re-arrange and factor out \(x^2: x^2(x^2−x−6)=0\) --> So one solution is 0 -> \(x^2\)
2.) Use discriminant for the left equation \((x^2−x−6)=0\): \(b^2 - 4ac\) --> 1-(4*1*(-6)) -> 25 -> Since 25 is positive the left equation has two solutions
3.) 1.) + 2.) = 3 Solutions


You should find the actual roots and find out whether all of them are valid. Only 2 of them are valid for the equation at hand. Please refer to the discussion on previous 2 pages.
_________________

New to the Math Forum?
Please read this: Ultimate GMAT Quantitative Megathread | All You Need for Quant | PLEASE READ AND FOLLOW: 12 Rules for Posting!!!

Resources:
GMAT Math Book | Triangles | Polygons | Coordinate Geometry | Factorials | Circles | Number Theory | Remainders; 8. Overlapping Sets | PDF of Math Book; 10. Remainders | GMAT Prep Software Analysis | SEVEN SAMURAI OF 2012 (BEST DISCUSSIONS) | Tricky questions from previous years.

Collection of Questions:
PS: 1. Tough and Tricky questions; 2. Hard questions; 3. Hard questions part 2; 4. Standard deviation; 5. Tough Problem Solving Questions With Solutions; 6. Probability and Combinations Questions With Solutions; 7 Tough and tricky exponents and roots questions; 8 12 Easy Pieces (or not?); 9 Bakers' Dozen; 10 Algebra set. ,11 Mixed Questions, 12 Fresh Meat

DS: 1. DS tough questions; 2. DS tough questions part 2; 3. DS tough questions part 3; 4. DS Standard deviation; 5. Inequalities; 6. 700+ GMAT Data Sufficiency Questions With Explanations; 7 Tough and tricky exponents and roots questions; 8 The Discreet Charm of the DS; 9 Devil's Dozen!!!; 10 Number Properties set., 11 New DS set.


What are GMAT Club Tests?
Extra-hard Quant Tests with Brilliant Analytics

Kudos [?]: 129505 [0], given: 12201

Intern
Intern
avatar
Joined: 17 Mar 2016
Posts: 1

Kudos [?]: [0], given: 16

GMAT ToolKit User
Re D01-13 [#permalink]

Show Tags

New post 19 Apr 2016, 13:07
I think this is a high-quality question and I agree with explanation.

Kudos [?]: [0], given: 16

Intern
Intern
avatar
Joined: 19 Jul 2016
Posts: 11

Kudos [?]: 2 [0], given: 5

Re: D01-13 [#permalink]

Show Tags

New post 20 Jul 2016, 01:24
I am still not able to convince my self that -2 is not the root of the given equation. Because as per my knowledge this should have been the one solution. Now, the dilemma is what i will do in similar questions. :(

Kudos [?]: 2 [0], given: 5

Senior Manager
Senior Manager
User avatar
Joined: 31 Mar 2016
Posts: 406

Kudos [?]: 78 [0], given: 197

Location: India
Concentration: Operations, Finance
GMAT 1: 670 Q48 V34
GPA: 3.8
WE: Operations (Commercial Banking)
GMAT ToolKit User Premium Member
Re D01-13 [#permalink]

Show Tags

New post 07 Aug 2016, 02:49
I think this is a high-quality question and I agree with explanation.

Kudos [?]: 78 [0], given: 197

Intern
Intern
avatar
Joined: 02 Sep 2016
Posts: 10

Kudos [?]: [0], given: 0

Re: D01-13 [#permalink]

Show Tags

New post 21 Sep 2016, 10:38
how did the following question become x*4-x*3-6x*2=0?

Kudos [?]: [0], given: 0

Expert Post
Math Expert
User avatar
V
Joined: 02 Sep 2009
Posts: 41913

Kudos [?]: 129505 [0], given: 12201

Re: D01-13 [#permalink]

Show Tags

New post 22 Sep 2016, 00:59
manchitkapoor wrote:
how did the following question become x*4-x*3-6x*2=0?


It does not.


Take \(x=\sqrt[4]{x^3+6x^2}\) to the 4th power to get \(x^4=x^3+6x^2\), which when re-arranged becomes \(x^4-x^3-6x^2=0\). It's x to the 4th power, minus x cubed, minus 6 times x squared, equal 0.
_________________

New to the Math Forum?
Please read this: Ultimate GMAT Quantitative Megathread | All You Need for Quant | PLEASE READ AND FOLLOW: 12 Rules for Posting!!!

Resources:
GMAT Math Book | Triangles | Polygons | Coordinate Geometry | Factorials | Circles | Number Theory | Remainders; 8. Overlapping Sets | PDF of Math Book; 10. Remainders | GMAT Prep Software Analysis | SEVEN SAMURAI OF 2012 (BEST DISCUSSIONS) | Tricky questions from previous years.

Collection of Questions:
PS: 1. Tough and Tricky questions; 2. Hard questions; 3. Hard questions part 2; 4. Standard deviation; 5. Tough Problem Solving Questions With Solutions; 6. Probability and Combinations Questions With Solutions; 7 Tough and tricky exponents and roots questions; 8 12 Easy Pieces (or not?); 9 Bakers' Dozen; 10 Algebra set. ,11 Mixed Questions, 12 Fresh Meat

DS: 1. DS tough questions; 2. DS tough questions part 2; 3. DS tough questions part 3; 4. DS Standard deviation; 5. Inequalities; 6. 700+ GMAT Data Sufficiency Questions With Explanations; 7 Tough and tricky exponents and roots questions; 8 The Discreet Charm of the DS; 9 Devil's Dozen!!!; 10 Number Properties set., 11 New DS set.


What are GMAT Club Tests?
Extra-hard Quant Tests with Brilliant Analytics

Kudos [?]: 129505 [0], given: 12201

Intern
Intern
avatar
Joined: 12 Nov 2016
Posts: 13

Kudos [?]: 2 [0], given: 3

Location: Nigeria
GMAT 1: 520 Q43 V27
GPA: 2.66
CAT Tests
Re: D01-13 [#permalink]

Show Tags

New post 25 Nov 2016, 08:17
This is a nice question. I forgot that 0 is a multiple of 9. :)

Kudos [?]: 2 [0], given: 3

Manager
Manager
avatar
G
Joined: 14 Oct 2012
Posts: 167

Kudos [?]: 50 [0], given: 944

Premium Member Reviews Badge CAT Tests
D01-13 [#permalink]

Show Tags

New post 01 Apr 2017, 09:38
Bunuel wrote:
manchitkapoor wrote:
how did the following question become x*4-x*3-6x*2=0?


It does not.


Take \(x=\sqrt[4]{x^3+6x^2}\) to the 4th power to get \(x^4=x^3+6x^2\), which when re-arranged becomes \(x^4-x^3-6x^2=0\). It's x to the 4th power, minus x cubed, minus 6 times x squared, equal 0.


I think this should clarifies everybody's confusion regarding the answer, i hope everyone understands how we got 0,3,(-2)

\(x=\sqrt[4]{x^3+6x^2}\)
x=0
\(0=\sqrt[4]{0^3+6*0^2}\)
\(0=\sqrt[4]{0}\)
\(0=0\)

\(x=\sqrt[4]{x^3+6x^2}\)
x=3
\(3=\sqrt[4]{3^3+6*3^2}\)
\(3=\sqrt[4]{27+6*9}\)
\(3=\sqrt[4]{27+54}\)
\(3=\sqrt[4]{81}\)
\(3=3\)

\(x=\sqrt[4]{x^3+6x^2}\)
x=(-2)
\((-2)=\sqrt[4]{(-2)^3+6*(-2)^2}\)
\((-2)=\sqrt[4]{-8+6*4}\)
\((-2)=\sqrt[4]{-8+24}\)
\((-2)=\sqrt[4]{16}\)
\((-2) =| 2\)
Thus solution x = (-2) isn't applicable.
Answer: 3+0 = 3

Kudos [?]: 50 [0], given: 944

Intern
Intern
avatar
B
Joined: 26 Sep 2016
Posts: 23

Kudos [?]: [0], given: 30

Reviews Badge
Re: D01-13 [#permalink]

Show Tags

New post 12 Apr 2017, 04:49
And here we go again. Sometimes i feel as if GMAT has it's own version of math that goes against universal one. I understand that on verbal there can be a whole lot of inerprteations of rules, simply because it is VERBAL, as in not a precise science which is basically a human imagination. But math has to be precise. And now, according to e-GMAT -b^m if m is even --> positive number and you are stating that −2^4=−16 and i made a whole lot of mistakes when practicing quant from both OG and scholaranium that involved sqr.root of a number, because i didn't include the negative value as well. Can comeone give a link or a screenshot of an OG question where when we take sqr root we don't consider the negative value?

Kudos [?]: [0], given: 30

Expert Post
Math Expert
User avatar
V
Joined: 02 Sep 2009
Posts: 41913

Kudos [?]: 129505 [0], given: 12201

Re: D01-13 [#permalink]

Show Tags

New post 12 Apr 2017, 04:58
stan3544 wrote:
And here we go again. Sometimes i feel as if GMAT has it's own version of math that goes against universal one. I understand that on verbal there can be a whole lot of inerprteations of rules, simply because it is VERBAL, as in not a precise science which is basically a human imagination. But math has to be precise. And now, according to e-GMAT -b^m if m is even --> positive number and you are stating that −2^4=−16 and i made a whole lot of mistakes when practicing quant from both OG and scholaranium that involved sqr.root of a number, because i didn't include the negative value as well. Can comeone give a link or a screenshot of an OG question where when we take sqr root we don't consider the negative value?


Not sure I understand what you mean but GMAT doe not have its own math. That's simply not correct. The only thing is that GMAT deals with only Real Numbers: Integers, Fractions and Irrational Numbers, so no imaginary numbers. That's why the even roots from negative numbers are not defined for the GMAT.

As for your example:

(-2)^4 = 16 but -2^4 = -16, this is true generally not only for the GMAT.
_________________

New to the Math Forum?
Please read this: Ultimate GMAT Quantitative Megathread | All You Need for Quant | PLEASE READ AND FOLLOW: 12 Rules for Posting!!!

Resources:
GMAT Math Book | Triangles | Polygons | Coordinate Geometry | Factorials | Circles | Number Theory | Remainders; 8. Overlapping Sets | PDF of Math Book; 10. Remainders | GMAT Prep Software Analysis | SEVEN SAMURAI OF 2012 (BEST DISCUSSIONS) | Tricky questions from previous years.

Collection of Questions:
PS: 1. Tough and Tricky questions; 2. Hard questions; 3. Hard questions part 2; 4. Standard deviation; 5. Tough Problem Solving Questions With Solutions; 6. Probability and Combinations Questions With Solutions; 7 Tough and tricky exponents and roots questions; 8 12 Easy Pieces (or not?); 9 Bakers' Dozen; 10 Algebra set. ,11 Mixed Questions, 12 Fresh Meat

DS: 1. DS tough questions; 2. DS tough questions part 2; 3. DS tough questions part 3; 4. DS Standard deviation; 5. Inequalities; 6. 700+ GMAT Data Sufficiency Questions With Explanations; 7 Tough and tricky exponents and roots questions; 8 The Discreet Charm of the DS; 9 Devil's Dozen!!!; 10 Number Properties set., 11 New DS set.


What are GMAT Club Tests?
Extra-hard Quant Tests with Brilliant Analytics

Kudos [?]: 129505 [0], given: 12201

Intern
Intern
avatar
B
Joined: 26 Sep 2016
Posts: 23

Kudos [?]: [0], given: 30

Reviews Badge
Re: D01-13 [#permalink]

Show Tags

New post 12 Apr 2017, 05:58
Bunuel wrote:
stan3544 wrote:
And here we go again. Sometimes i feel as if GMAT has it's own version of math that goes against universal one. I understand that on verbal there can be a whole lot of inerprteations of rules, simply because it is VERBAL, as in not a precise science which is basically a human imagination. But math has to be precise. And now, according to e-GMAT -b^m if m is even --> positive number and you are stating that −2^4=−16 and i made a whole lot of mistakes when practicing quant from both OG and scholaranium that involved sqr.root of a number, because i didn't include the negative value as well. Can comeone give a link or a screenshot of an OG question where when we take sqr root we don't consider the negative value?


Not sure I understand what you mean but GMAT doe not have its own math. That's simply not correct. The only thing is that GMAT deals with only Real Numbers: Integers, Fractions and Irrational Numbers, so no imaginary numbers. That's why the even roots from negative numbers are not defined for the GMAT.

As for your example:

(-2)^4 = 16 but -2^4 = -16, this is true generally not only for the GMAT.


Hey Bunuel,

Now i am totally confused. Yes it is obvious and universally understood that sqr.root of negative number is not a real number, basically it doesn't exist, why? Because no negative number raised to an even power will ever give us a negative result, yet according to your example -2^4 = -16, so we know that the number -2 raised to the power 4 gives us -16, isn't it a paradox? Now, according to the exponent rules: (-2)^4 = (-2^1)^4 = -2*(-2)*(-2)*(-2) right? Now according to your interpretation -2^4 is not the same, so it basically means -2*2*2*2, which doesn't make sense, because this goes against the whole idea behind exponents, which is: we take a number and multiply by ITSELF n times. So the correct way to write it would be -(2^4) = -16 or -(-2^4) = -16. Now back to the issue at hand: logically 2^2=4 as well as -2*(-2)=4, which is (-2)^2= 4, now i don't see why sqr.root of 4 can only be 2 and not -2 as well.

Kudos [?]: [0], given: 30

Expert Post
Math Expert
User avatar
V
Joined: 02 Sep 2009
Posts: 41913

Kudos [?]: 129505 [0], given: 12201

Re: D01-13 [#permalink]

Show Tags

New post 12 Apr 2017, 06:05
stan3544 wrote:
Bunuel wrote:
stan3544 wrote:
And here we go again. Sometimes i feel as if GMAT has it's own version of math that goes against universal one. I understand that on verbal there can be a whole lot of inerprteations of rules, simply because it is VERBAL, as in not a precise science which is basically a human imagination. But math has to be precise. And now, according to e-GMAT -b^m if m is even --> positive number and you are stating that −2^4=−16 and i made a whole lot of mistakes when practicing quant from both OG and scholaranium that involved sqr.root of a number, because i didn't include the negative value as well. Can comeone give a link or a screenshot of an OG question where when we take sqr root we don't consider the negative value?


Not sure I understand what you mean but GMAT doe not have its own math. That's simply not correct. The only thing is that GMAT deals with only Real Numbers: Integers, Fractions and Irrational Numbers, so no imaginary numbers. That's why the even roots from negative numbers are not defined for the GMAT.

As for your example:

(-2)^4 = 16 but -2^4 = -16, this is true generally not only for the GMAT.


Hey Bunuel,

Now i am totally confused. Yes it is obvious and universally understood that sqr.root of negative number is not a real number, basically it doesn't exist, why? Because no negative number raised to an even power will ever give us a negative result, yet according to your example -2^4 = -16, so we know that the number -2 raised to the power 4 gives us -16, isn't it a paradox? Now, according to the exponent rules: (-2)^4 = (-2^1)^4 = -2*(-2)*(-2)*(-2) right? Now according to your interpretation -2^4 is not the same, so it basically means -2*2*2*2, which doesn't make sense, because this goes against the whole idea behind exponents, which is: we take a number and multiply by ITSELF n times. So the correct way to write it would be -(2^4) = -16 or -(-2^4) = -16. Now back to the issue at hand: logically 2^2=4 as well as -2*(-2)=4, which is (-2)^2= 4, now i don't see why sqr.root of 4 can only be 2 and not -2 as well.


-2^4 = -(2^4) = -16. It's order of operations thing.

As for the square roots: I tried to explain it several times on previous pages but I'll try this one last time:

When the GMAT provides the square root sign for an even root, such as \(\sqrt{x}\) or \(\sqrt[4]{x}\), then the only accepted answer is the positive root.

That is, \(\sqrt{25}=5\), NOT +5 or -5. Even roots have only a positive value on the GMAT.

In contrast, the equation \(x^2=25\) has TWO solutions, +5 and -5.

If it's still unclear or confusing then probably it's better to start from basics and brush-up fundamentals or enrol into a class.
_________________

New to the Math Forum?
Please read this: Ultimate GMAT Quantitative Megathread | All You Need for Quant | PLEASE READ AND FOLLOW: 12 Rules for Posting!!!

Resources:
GMAT Math Book | Triangles | Polygons | Coordinate Geometry | Factorials | Circles | Number Theory | Remainders; 8. Overlapping Sets | PDF of Math Book; 10. Remainders | GMAT Prep Software Analysis | SEVEN SAMURAI OF 2012 (BEST DISCUSSIONS) | Tricky questions from previous years.

Collection of Questions:
PS: 1. Tough and Tricky questions; 2. Hard questions; 3. Hard questions part 2; 4. Standard deviation; 5. Tough Problem Solving Questions With Solutions; 6. Probability and Combinations Questions With Solutions; 7 Tough and tricky exponents and roots questions; 8 12 Easy Pieces (or not?); 9 Bakers' Dozen; 10 Algebra set. ,11 Mixed Questions, 12 Fresh Meat

DS: 1. DS tough questions; 2. DS tough questions part 2; 3. DS tough questions part 3; 4. DS Standard deviation; 5. Inequalities; 6. 700+ GMAT Data Sufficiency Questions With Explanations; 7 Tough and tricky exponents and roots questions; 8 The Discreet Charm of the DS; 9 Devil's Dozen!!!; 10 Number Properties set., 11 New DS set.


What are GMAT Club Tests?
Extra-hard Quant Tests with Brilliant Analytics

Kudos [?]: 129505 [0], given: 12201

Intern
Intern
avatar
B
Joined: 26 Sep 2016
Posts: 23

Kudos [?]: [0], given: 30

Reviews Badge
Re: D01-13 [#permalink]

Show Tags

New post 12 Apr 2017, 07:37
Thanks for the explanation

Maybe i wasn't able to explain clearly what i was confused about, but i found the answer on the Magoosh website, boldfaced is the explanation i needed: The equation x^2 = 16 has two solutions, x = +4 and x = -4, because 4^2 = 16 and (-4)^2 = 16, and the GMAT will impale you for only remembering one of those two. At the same time, sqrt{16} has only one output: sqrt{16} = +4 only. When you yourself undo a square by taking a square root, that’s a process that results in two possibilities, but when you see this symbol as such, printed as part of the problem, it means find the positive square root only.

Hope this clears all the doubts for everyone.

Kudos [?]: [0], given: 30

Senior Manager
Senior Manager
User avatar
G
Joined: 26 Aug 2016
Posts: 465

Kudos [?]: 59 [0], given: 49

Location: India
Schools: Duke '20, Tepper '20
GMAT 1: 690 Q50 V33
GMAT 2: 700 Q50 V33
GPA: 4
WE: Consulting (Consulting)
Premium Member CAT Tests
Re: D01-13 [#permalink]

Show Tags

New post 01 May 2017, 09:38
Bunuel wrote:
Official Solution:

If \(x=\sqrt[4]{x^3+6x^2}\), then the sum of all possible solutions for x is:

A. \(-2\)
B. \(0\)
C. \(1\)
D. \(3\)
E. \(5\)


Take the given expression to the 4th power: \(x^4=x^3+6x^2\);

Re-arrange and factor out x^2: \(x^2(x^2-x-6)=0\);

Factorize: \(x^2(x-3)(x+2)=0\);

So, the roots are \(x=0\), \(x=3\) and \(x=-2\). But \(x\) cannot be negative as it equals to the even (4th) root of some expression (\(\sqrt{expression}\geq{0}\)), thus only two solution are valid \(x=0\) and \(x=3\).

The sum of all possible solutions for x is 0+3=3.


Answer: D


Thank you for this valuable info. Because in engineering we used to consider root(4) = + / - 2 . Now, I know that GMAT only considers positive values for even roots. :) . Ahh i screwed up one question in Main GMAT because of my ignorance in regards to this knowledge.

Kudos [?]: 59 [0], given: 49

1 KUDOS received
Intern
Intern
avatar
B
Joined: 17 Nov 2016
Posts: 15

Kudos [?]: 2 [1], given: 10

CAT Tests
D01-13 [#permalink]

Show Tags

New post 30 May 2017, 23:18
1
This post received
KUDOS
stan3544 wrote:
And here we go again. Sometimes i feel as if GMAT has it's own version of math that goes against universal one. I understand that on verbal there can be a whole lot of inerprteations of rules, simply because it is VERBAL, as in not a precise science which is basically a human imagination. But math has to be precise. And now, according to e-GMAT -b^m if m is even --> positive number and you are stating that −2^4=−16 and i made a whole lot of mistakes when practicing quant from both OG and scholaranium that involved sqr.root of a number, because i didn't include the negative value as well. Can comeone give a link or a screenshot of an OG question where when we take sqr root we don't consider the negative value?


The gmat doesn't have its own version of math. The square root is a function, that's why it is always positive. As a function, it can't take a positive and a negative value (if it did, it wouldn't be a function, you can look at the graph to check that out).

When you solve x^2 = 4, applying the square root function and assuming two results for x is incorrect, because you would only get x = 2. The formal and correct method is:
x^2 = 4
x^2 - 4 =0
(x + 2)(x - 2)=0 and from here get both results for x.

Kudos [?]: 2 [1], given: 10

Expert Post
Math Expert
User avatar
V
Joined: 02 Sep 2009
Posts: 41913

Kudos [?]: 129505 [0], given: 12201

Re: D01-13 [#permalink]

Show Tags

New post 30 May 2017, 23:21
CristianJuarez wrote:
stan3544 wrote:
And here we go again. Sometimes i feel as if GMAT has it's own version of math that goes against universal one. I understand that on verbal there can be a whole lot of inerprteations of rules, simply because it is VERBAL, as in not a precise science which is basically a human imagination. But math has to be precise. And now, according to e-GMAT -b^m if m is even --> positive number and you are stating that −2^4=−16 and i made a whole lot of mistakes when practicing quant from both OG and scholaranium that involved sqr.root of a number, because i didn't include the negative value as well. Can comeone give a link or a screenshot of an OG question where when we take sqr root we don't consider the negative value?


The gmat doesn't have its own version of math. The square root is a function, that's why it is always positive. As a function, it can't take a positive and a negative value (if it did, it wouldn't be a function, you can look at the graph to check that out).

When you solve x^2 = 4, applying the square root function and assuming two results for x is incorrect, because you would only get x = 2. The formal and correct method is:
x^2 = 4
x^2 - 4 =0
(x + 2)(x - 2)=0 and from here get both results for x.


That's correct. + 1.

Another way of solving x^2 = 4 would be:

\(x = \sqrt{4}=2\) or \(x = -\sqrt{4}=-2\).
_________________

New to the Math Forum?
Please read this: Ultimate GMAT Quantitative Megathread | All You Need for Quant | PLEASE READ AND FOLLOW: 12 Rules for Posting!!!

Resources:
GMAT Math Book | Triangles | Polygons | Coordinate Geometry | Factorials | Circles | Number Theory | Remainders; 8. Overlapping Sets | PDF of Math Book; 10. Remainders | GMAT Prep Software Analysis | SEVEN SAMURAI OF 2012 (BEST DISCUSSIONS) | Tricky questions from previous years.

Collection of Questions:
PS: 1. Tough and Tricky questions; 2. Hard questions; 3. Hard questions part 2; 4. Standard deviation; 5. Tough Problem Solving Questions With Solutions; 6. Probability and Combinations Questions With Solutions; 7 Tough and tricky exponents and roots questions; 8 12 Easy Pieces (or not?); 9 Bakers' Dozen; 10 Algebra set. ,11 Mixed Questions, 12 Fresh Meat

DS: 1. DS tough questions; 2. DS tough questions part 2; 3. DS tough questions part 3; 4. DS Standard deviation; 5. Inequalities; 6. 700+ GMAT Data Sufficiency Questions With Explanations; 7 Tough and tricky exponents and roots questions; 8 The Discreet Charm of the DS; 9 Devil's Dozen!!!; 10 Number Properties set., 11 New DS set.


What are GMAT Club Tests?
Extra-hard Quant Tests with Brilliant Analytics

Kudos [?]: 129505 [0], given: 12201

Re: D01-13   [#permalink] 30 May 2017, 23:21

Go to page   Previous    1   2   3    Next  [ 44 posts ] 

Display posts from previous: Sort by

D01-13

  new topic post reply Question banks Downloads My Bookmarks Reviews Important topics  

Moderators: Bunuel, Vyshak



GMAT Club MBA Forum Home| About| Terms and Conditions| GMAT Club Rules| Contact| Sitemap

Powered by phpBB © phpBB Group | Emoji artwork provided by EmojiOne

Kindly note that the GMAT® test is a registered trademark of the Graduate Management Admission Council®, and this site has neither been reviewed nor endorsed by GMAC®.