Help with simple maths problem

Question

Help needed with the following:

(x-y)^2 = 0.

I understand that this translates to (x-y)(x-y) = 0. But kaplan says that this is the same as (x-y) = 0, why is this.

Thanks

aurobindo · Answer

can we give any other value to (x - y), and ensure that (x-y)(x-y) = 0 ? :lol:

AdrianG · Answer

Actually, (x-y)^2 = x^2 - 2xy + y^2

GMAT? · Answer

This is what I thought it translated to as well:

(x-y)^2 = x^2 - 2xy + y^2

The whole question is:

Does x = y

(1) x^2 - y^2 = 0
(2) (x-y)^2 = 0

I know that the answer if B. 

With (1): x^2 = y^2 but that does not mean x = y as 2^2 and -2^2 both = 16.

With (2): (x-y)^2 = 0. So x^2 - 2xy + y^2 = 0, hence x^2 -2xy = -y^2 hence x=y.

Just was unsure how kaplan got that (x-y)(x-y) = 0 is the same as (x-y) = 0.

Thanks

burningskulls · Answer

In order to have (x-y)(x-y) equal 0, one of the two things you are multiplying must be equal to 0.

So either (x-y) or (x-y) has to be equal to 0.

And if one of them is, then the other one has to be as well.

Try working the logic using X * X = 0 (substitute X for x-y)

Hope that helps

Help with simple maths problem

Prep Toolkit

Top 5 GMAT Debrief Videos

615 to 715 in 15 Days (Ria's Strategies)

More than Quant/Verbal Abilities: Speed vs. Accuracy

745 with Only Self-Prep and GMAT Club

From 555 to 765: 210-point Improvement

Perfect 805 Score Debrief by Julia

My Rewards