Help with simple maths problem

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GMAT?: Senior | Next Rank: 100 Posts; Posts: 46; Joined: Fri Sep 29, 2006 10:04 am

by GMAT? » Thu Jan 11, 2007 7:26 am

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

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Source: Beat The GMAT — Quantitative Reasoning | Thu Jan 11, 2007 7:26 am

b00ndgl: Newbie | Next Rank: 10 Posts; Posts: 3; Joined: Mon Jan 08, 2007 9:39 am

by b00ndgl » Thu Jan 11, 2007 1:19 pm

If (x-y)^2 = (x-y)(x-y)=0, then we can immediately say that (x-y)=0. This equation consists of the multiplication of two terms that are the same, so we need only consider one of the terms (since they are both the same).

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chandooed: Newbie | Next Rank: 10 Posts; Posts: 1; Joined: Wed Jan 10, 2007 12:24 pm

Re: Help with simple maths problem

by chandooed » Thu Jan 11, 2007 1:26 pm

(x-y)^2=0;
apply sqrt on both sides of the '=' sign
sqrt [ (x-y)^2 ] = sqrt (0); ( sqrt of (x-y)^2 is (x-y) & sqrt of 0 is 0)
so, (x-y) = 0.

Hope this helps.

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wildrebel: Community Manager; Posts: 40; Joined: Mon Jun 26, 2006 11:59 pmFollowed by: 1 member

by wildrebel » Thu Jan 11, 2007 2:37 pm

In simpler terms,

if (x-y)^2 = 0,

that means (x-y)(x-y)=0

Simple logic- if ZERO is the product of two numbers, one or both of those numbers HAS to be ZERO.
For eg. (1)(0)=0, (0)(534)=0 or (0)(0)=0

In this case, since you're squaring (x-y), and the answer is 0, that means x-y HAS TO BE 0.

Other than the number 0, no other number can mathematically square to 0.

Hope that was easier to understand than lines of equations.

"Outside of a dog, a book is a man's best friend. Inside of a dog, it's too dark to read."
- Groucho Marx

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