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then (x+1/x)^2 - (x-1/x)^2 =

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by Anurag@Gurome » Tue Jul 17, 2012 10:36 pm
alex.gellatly wrote:If x does not equal 0, then (x+1/x)^2 - (x-1/x)^2 =
This can be solved in many ways,
Method 1:
(x + 1/x)² = (x² + 2 + 1/x²)
(x - 1/x)² = (x² - 2 + 1/x²)

Hence, (x + 1/x)² - (x - 1/x)² = 2 + 2 = 4

Method 2:
Let us assumes, (x + 1/x) = a and (x - 1/x) = b
Hence, (x + 1/x)² - (x - 1/x)² = (a² - b²) = (a - b)(a + b) = (2/x)*(2x) = 4

The correct answer is E.
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by GMATGuruNY » Wed Jul 18, 2012 12:03 pm
alex.gellatly wrote:If x does not equal 0, then (x+1/x)^2 - (x-1/x)^2 =

1/x
x
1
2
4
Let x=1.
Then ( x+1 / x )² - ( x-1 / x )² = ( 1+1 / 1 )² - ( 1-1 / 1 )² = 4-0 = 4.

The correct answer is E.
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by alex.gellatly » Wed Jul 25, 2012 12:58 am
GMATGuruNY wrote:
alex.gellatly wrote:If x does not equal 0, then (x+1/x)^2 - (x-1/x)^2 =

1/x
x
1
2
4
Let x=1.
Then ( x+1 / x )² - ( x-1 / x )² = ( 1+1 / 1 )² - ( 1-1 / 1 )² = 4-0 = 4.

The correct answer is E.
If we let x = 1, shouldn't the correct answer be 4x (not 4). I got 4x, which is not an option.
Thanks
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by dineshsaini88 » Fri Jul 27, 2012 11:05 am
if u got 4x with x=1 put x=1 in 4x .. u ll get 4 .
cheers :)
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by alex.gellatly » Sat Jul 28, 2012 10:52 pm
dineshsaini88 wrote:if u got 4x with x=1 put x=1 in 4x .. u ll get 4 .
cheers :)
God... I'm an idiot. Haha, thanks.
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