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Which of the following Equation is NOT equivalent to 25x^2=y^2-4?

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Which of the following Equation is NOT equivalent to 25x^2=y^2-4?  [#permalink]

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Which of the following Equation is NOT equivalent to 25x^2 = y^2 - 4?Which of the following Equation is NOT equivalent to 25x^2 = y^2 - 4?

A) 25x^2 + 4 = y^2
B) 75x^2 = 3y^2 - 12
C) 25x^2 = (y + 2)(y - 2)
D) 5x = y - 2
E) x^2 = (y^2 - 4)/25


This Question i have taken from Jamboree red book, and while searching over the internet i got to know it's a very old OG question,as per the answer sheet D is the answer, could someone please tell me why?
Thanks In Advance.

Originally posted by jaspreets on 01 Jul 2015, 03:01.
Last edited by Bunuel on 01 Jul 2015, 03:08, edited 1 time in total.
Edited the question.
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Re: Which of the following Equation is NOT equivalent to 25x^2=y^2-4?  [#permalink]

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New post 01 Jul 2015, 03:09
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jaspreets wrote:
Which of the following Equation is NOT equivalent to 25x^2 = y^2 - 4?Which of the following Equation is NOT equivalent to 25x^2 = y^2 - 4?

A) 25x^2 + 4 = y^2
B) 75x^2 = 3y^2 - 12
C) 25x^2 = (y + 2)(y - 2)
D) 5x = y - 2
E) x^2 = (y^2 - 4)/25


This Question i have taken from Jamboree red book, and while searching over the internet i got to know it's a very old OG question,as per the answer sheet D is the answer, could someone please tell me why?
Thanks In Advance.


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Hope it helps.
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Re: Which of the following Equation is NOT equivalent to 25x^2=y^2-4?  [#permalink]

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New post 01 Jul 2015, 03:13
jaspreets wrote:
Which of the following Equation is NOT equivalent to 25x^2 = y^2 - 4?Which of the following Equation is NOT equivalent to 25x^2 = y^2 - 4?

A) 25x^2 + 4 = y^2
B) 75x^2 = 3y^2 - 12
C) 25x^2 = (y + 2)(y - 2)
D) 5x = y - 2
E) x^2 = (y^2 - 4)/25


This Question i have taken from Jamboree red book, and while searching over the internet i got to know it's a very old OG question,as per the answer sheet D is the answer, could someone please tell me why?
Thanks In Advance.




I wonder why the answer is D?
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Re: Which of the following Equation is NOT equivalent to 25x^2=y^2-4?  [#permalink]

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New post 01 Jul 2015, 03:24
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jaspreets wrote:
jaspreets wrote:
Which of the following Equation is NOT equivalent to 25x^2 = y^2 - 4?Which of the following Equation is NOT equivalent to 25x^2 = y^2 - 4?

A) 25x^2 + 4 = y^2
B) 75x^2 = 3y^2 - 12
C) 25x^2 = (y + 2)(y - 2)
D) 5x = y - 2
E) x^2 = (y^2 - 4)/25


This Question i have taken from Jamboree red book, and while searching over the internet i got to know it's a very old OG question,as per the answer sheet D is the answer, could someone please tell me why?
Thanks In Advance.


I wonder why the answer is D?



Let's Solve the given equation first

25x^2 = y^2 - 4
i.e. (5x)^2 - y^2 = -4
i.e. y^2 - (5x)^2 = 4


Let's Check the Options:

A) 25x^2 + 4 = y^2
This equation can be re-written as
25x^2 = y^2 - 4 which is same as Equation given in question hence Option ELIMINATED

B) 75x^2 = 3y^2 - 12
Divide the equation by 3 on both sides, we get
25x^2 = y^2 - 4 which is same as Equation given in question hence Option ELIMINATED

C) 25x^2 = (y + 2)(y - 2)
This equation can be re-written as
25x^2 = y^2 -2y+2y - 4
i.e. 25x^2 = y^2 - 4 which is same as Equation given in question hence Option ELIMINATED

D) 5x = y - 2 Hence, The correct Answer Option

E) x^2 = (y^2 - 4)/25
Multiply the equation on both sides by 25
i.e. 25x^2 = y^2 - 4 which is same as Equation given in question hence Option ELIMINATED

I hope it helps!
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Re: Which of the following Equation is NOT equivalent to 25x^2=y^2-4?  [#permalink]

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New post 01 Jul 2015, 04:22
Option (A): It's a simple realignment of the original equation, so it's the same.

Option (B): Multiplied by 3, same.

Option (C): LHS is the same, RHS is expressed in a different form, (a^2 - b^2) = (a+b) (a-b). Same.

Option (D): y^2 - 4 is not equal to y-2, from Option (C) we can see that (y^2 - 4) = (y+2) (y-2). So this is not the same as the original equation.

Option (E): Multiplying both sides by 25 we get the original equation, so it's also the same.

So, we arrived at the solution in 2 ways.
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Re: Which of the following Equation is NOT equivalent to 25x^2=y^2-4?  [#permalink]

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New post 01 Jul 2015, 05:34
Writing down how each answer choice was different, I came up with:
A. Add four to both sides
B. Multiplied by three to both sides
C. RHS is the difference of squares, nothing changed
D. Only six operations can be done to expressions: add, subtract, multiply, divide, take root, or raise to a power. None of them will bring us to this answer choice.
E. Divided by 25 both sides

D.
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Re: Which of the following Equation is NOT equivalent to 25x^2=y^2-4?  [#permalink]

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New post 01 Jul 2015, 21:14
Hi jaspreets,

With this question, you can either...
1) Take the original equation and try to manipulate it so that it becomes 4 of the 5 answers
2) Take each answer choice and see if you can manipulate it to make it into the original equation.

With Answer D, we have...

5X = Y - 2

If we square both sides, we end up with....

(5X)^2 = (Y-2)^2
(5X)(5X) = (Y-2)(Y-2)

25X^2 = Y^2 - 4Y + 4

This is NOT a match for the original equation, so it's the answer that is NOT equivalent.

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Re: Which of the following Equation is NOT equivalent to 25x^2=y^2-4?  [#permalink]

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New post 09 Aug 2016, 06:30
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jaspreets wrote:
Which of the following equations is NOT equivalent to 25x² = y² - 4?

A) 25x² + 4 = y²
B) 75x² = 3y² - 12
C) 25x² = (y + 2)(y - 2)
D) 5x = y - 2
E) x² = (y² - 4)/25



Two small points to note:
1) This is actually an official question from the 10th edition of the Official Guide
2) This question requires us to check/test each answer choice. In these situations, always check the answer choices from E to A, because the correct answer is typically closer to the bottom than to the top.

For more on this strategy, see my article: http://www.gmatprepnow.com/articles/han ... -questions

Cheers,
Brent
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Re: Which of the following Equation is NOT equivalent to 25x^2=y^2-4?  [#permalink]

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New post 28 Oct 2018, 17:22
jaspreets wrote:
Which of the following Equation is NOT equivalent to 25x^2 = y^2 - 4?Which of the following Equation is NOT equivalent to 25x^2 = y^2 - 4?

A) 25x^2 + 4 = y^2
B) 75x^2 = 3y^2 - 12
C) 25x^2 = (y + 2)(y - 2)
D) 5x = y - 2
E) x^2 = (y^2 - 4)/25


Let’s check each answer choice:

Choice A. If we move -4 to the left side of the given equation, we will obtain 25x^2 + 4 = y^2. Choice A is equivalent.

Choice B. If we multiply each side of the given equation by 3, we will obtain 75x^2 = 3y^2 - 12. Choice B is equivalent.

Choice C. If we factor the right hand side of the equation, we obtain 25x^2 = (y + 2)(y - 2). Choice C is equivalent.

Choice D. Since there is no way to manipulate 5x = y - 2 to equal 25^2 = y^2 - 4, we see that answer choice D is correct.

Choice E. If we divide each side of the given equation by 25, we obtain x^2 = (y^2 - 4)/25. Choice E is equivalent.

Answer: D
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Re: Which of the following Equation is NOT equivalent to 25x^2=y^2-4? &nbs [#permalink] 28 Oct 2018, 17:22
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