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.

It appears that you are browsing the GMAT Club forum unregistered!

Signing up is free, quick, and confidential.
Join other 500,000 members and get the full benefits of GMAT Club

Registration gives you:

Tests

Take 11 tests and quizzes from GMAT Club and leading GMAT prep companies such as Manhattan GMAT,
Knewton, and others. All are free for GMAT Club members.

Applicant Stats

View detailed applicant stats such as GPA, GMAT score, work experience, location, application
status, and more

Books/Downloads

Download thousands of study notes,
question collections, GMAT Club’s
Grammar and Math books.
All are free!

Thank you for using the timer!
We noticed you are actually not timing your practice. Click the START button first next time you use the timer.
There are many benefits to timing your practice, including:

seems you have correct OA. but how? could you explain?

This is my logic---->

We know that x<0, then -x > 0. In other words, -x*|x| = +x^2

so, sqrt(-x*|x|) = sqrt(x^2) = +x or -x. but since it is GIVEN that x < 0, answer should be "-x".

(For any sqrt, answer is always "+" or "-" ; but if some condition is given, we can arrive at whether "+" OR "-")

but we cannot have -x as one of the value of sqrt(x^2) because sqrt(x^2) has only one value that is x. any square under radical sign has only +ve value.

How do you say that? For example, "25" is a square of "5" & also of "-5".
sqrt(25) = +5 or -5. I didn't get your point.

seems you have correct OA. but how? could you explain?

This is my logic---->

We know that x<0, then -x > 0. In other words, -x*|x| = +x^2

so, sqrt(-x*|x|) = sqrt(x^2) = +x or -x. but since it is GIVEN that x < 0, answer should be "-x".

(For any sqrt, answer is always "+" or "-" ; but if some condition is given, we can arrive at whether "+" OR "-")

I am with you untill

sqrt(-x*|x|) = sqrt(x^2) = +x or -x.

so sqrt(-x*|x|) is -ve or +ve

and its absolute value is |x|

x or -x

how do you conclude that the value of the expression sqrt(-x*|x|) is -x?

OD,
Frankly speaking, I'm not very comfortable with this problem. Ideally, answer should be "+/-x", but since it was already mentioned that x<0, (and most important: answer choice has both +x & -x, WE HAVE TO SELECT ONE CHOICE) the value that I selected is "-x"

For example, if we are solving sqrt(a) for something like age of a person, -ve value wouldn't make sense, we have to select +ve value.

This is my logic----> We know that x<0, then -x > 0. In other words, -x*|x| = +x^2 so, sqrt(-x*|x|) = sqrt(x^2) = +x or -x. but since it is GIVEN that x < 0, answer should be "-x".

(For any sqrt, answer is always "+" or "-" ; but if some condition is given, we can arrive at whether "+" OR "-")

but we cannot have -x as one of the value of sqrt(x^2) because sqrt(x^2) has only one value that is x. any square under radical sign has only +ve value.

How do you say that? For example, "25" is a square of "5" & also of "-5". sqrt(25) = +5 or -5. I didn't get your point.

lets see the following examples:

(I) x^2 = 25
(II) x = square root 25

these two are different conditions. so,

from (I), the value of x = + or - 5
from (II), the value of x can only be +5.

This is my logic----> We know that x<0, then -x > 0. In other words, -x*|x| = +x^2 so, sqrt(-x*|x|) = sqrt(x^2) = +x or -x. but since it is GIVEN that x < 0, answer should be "-x".

(For any sqrt, answer is always "+" or "-" ; but if some condition is given, we can arrive at whether "+" OR "-")

but we cannot have -x as one of the value of sqrt(x^2) because sqrt(x^2) has only one value that is x. any square under radical sign has only +ve value.

How do you say that? For example, "25" is a square of "5" & also of "-5". sqrt(25) = +5 or -5. I didn't get your point.

lets see the following examples:

(I) x^2 = 25 (II) x = square root 25

these two are different conditions. so,

from (I), the value of x = + or - 5 from (II), the value of x can only be +5.

further to my replies, i have seen somewhere in OG that sqrt (x) = +x only. i will post the same when i find.

What is the difference between (I) & (II)? I guess we arrive on (II) from (i) itself. I have a very uneasy feeling on this.

if x^2 = 25, x can be both +ve and -ve but if x = square root (25) x can only be 5, not -5. thats it. i told you it is in OG but where? i am trying to find it. once i get it, i will let you know.

This is my logic----> We know that x<0, then -x > 0. In other words, -x*|x| = +x^2 so, sqrt(-x*|x|) = sqrt(x^2) = +x or -x. but since it is GIVEN that x < 0, answer should be "-x".

(For any sqrt, answer is always "+" or "-" ; but if some condition is given, we can arrive at whether "+" OR "-")

but we cannot have -x as one of the value of sqrt(x^2) because sqrt(x^2) has only one value that is x. any square under radical sign has only +ve value.

How do you say that? For example, "25" is a square of "5" & also of "-5". sqrt(25) = +5 or -5. I didn't get your point.

lets see the following examples:

(I) x^2 = 25 (II) x = square root 25

these two are different conditions. so,

from (I), the value of x = + or - 5 from (II), the value of x can only be +5.

Square root of 25 is 5 as far as Gmat is concerned( it can be -5 of course, but not in Gmat)

You aren't right. The square root of a negative number isn't mathematically defined.

As Professor said:

(I) x^2 = 25
(II) x = square root 25

Statement II says that x has the value 5 and nothing else. Per definition you can take the square root soleily of a positive number or 0. Negative values aren't defined.

The thing why we consider -5 and +5 in statement I is that a number squared always yields a positive value, you know that of course. In two we don't square a number, and if we would we already knew that x is positive since it is sqrt25.

Of course if you consider sqrt (x^2) x can be positive or negative.

The square root of a negative number isn't mathematically defined.

As Professor said: (I) x^2 = 25 (II) x = square root 25

Statement II says that x has the value 5 and nothing else. Per definition you can take the square root soleily of a positive number or 0. Negative values aren't defined.

The thing why we consider -5 and +5 in statement I is that a number squared always yields a positive value, you know that of course. In two we don't square a number, and if we would we already knew that x is positive since it is sqrt25.

the important concept is: sqrt (x) has only one value i.e. +ve.

The square root of a negative number isn't mathematically defined.

As Professor said: (I) x^2 = 25 (II) x = square root 25

Statement II says that x has the value 5 and nothing else. Per definition you can take the square root soleily of a positive number or 0. Negative values aren't defined.

The thing why we consider -5 and +5 in statement I is that a number squared always yields a positive value, you know that of course. In two we don't square a number, and if we would we already knew that x is positive since it is sqrt25.

the important concept is: sqrt (x) has only one value i.e. +ve.

x = sqrt (25) = only 5. x^2 = 25 = 5 or -5.

i really don't understand the thinking behind this. why would sqrt have only one value?

BUT if you wanna go and check high math books,you can see that it can be -5.

What I dont understand : Why you guys lose time with unimportant stuff. Look at my solution. The answer to the original question is -x. And that is it. It has nothing to do with sqrt of 25 = 5 or -5!

p.s: By the way, if is only correct if it is used to convey the meaning of a possibility. Whether is always correct when you talk about alternatives.

BUT if you wanna go and check high math books,you can see that it can be -5.

What I dont understand : Why you guys lose time with unimportant stuff. Look at my solution. The answer to the original question is -x. And that is it. It has nothing to do with sqrt of 25 = 5 or -5!

p.s: By the way, if is only correct if it is used to convey the meaning of a possibility. Whether is always correct when you talk about alternatives.

If it's unimportant you don't have to bother replying the thread.

Square root of any positive number is a positive number. When we say x^2=a, we know that x=+/-sqrt(a). You can see that sqrt(a) itself is positive, but x could be positive sqrt(a) or negative sqrt(a).

Using an example, say x^2=25. We know that x=+/-sqrt(25), where sqrt(25)=5.

Hope this helps. _________________

Keep on asking, and it will be given you;
keep on seeking, and you will find;
keep on knocking, and it will be opened to you.

Just to End this discussion let me quote from the bible (OG-11, Page 126)

9. Absolute Value
The absolute value of x is denoted |x|, is defined to be x if x>=0 and â€“x is x<0. Note that sqrt(x^2) denotes that nonnegative square root of x^2 and so sqrt(x^2) = |x|

Following this answer of the question should be â€“x, as x is already negative and we need positive answer.

Look at the options, you know that 2 and 3 can be thrown out right away. sqrt(x) is wrong because for GMAT only positive number can be inside a square root. Compare 1 and 4, you want a positive number, which would be -x since x is negative. _________________

Keep on asking, and it will be given you;
keep on seeking, and you will find;
keep on knocking, and it will be opened to you.

Look at the options, you know that 2 and 3 can be thrown out right away. sqrt(x) is wrong because for GMAT only positive number can be inside a square root. Compare 1 and 4, you want a positive number, which would be -x since x is negative.

I guess this is how I arrived at my answer -x
But I was totally confused with what is needed in GMAT etc.

Anyways, thanks Hong

Cheers

gmatclubot

Re: absolute value
[#permalink]
21 Mar 2006, 04:37

Check out this awesome article about Anderson on Poets Quants, http://poetsandquants.com/2015/01/02/uclas-anderson-school-morphs-into-a-friendly-tech-hub/ . Anderson is a great place! Sorry for the lack of updates recently. I...

As you leave central, bustling Tokyo and head Southwest the scenery gradually changes from urban to farmland. You go through a tunnel and on the other side all semblance...

Ghibli studio’s Princess Mononoke was my first exposure to Japan. I saw it at a sleepover with a neighborhood friend after playing some video games and I was...