Help with this PSAT Question?

Test Preparation SAT Preparation
1

<p>If (x+y)^2-(x-y)^2=84 and x and y are both positive numbers, which of the following could be a value of x and y?
a)10
b)12
c)14
d)16
e)18
Thanks!</p>

2

<p>(x+y)^2-(x-y)^2=84</p>

<p>(x^2 + 2xy + y^2) - (x^2- 2xy+ y^2) = 84</p>

<p>4xy = 84</p>

<p>xy = 21</p>

<p>x can be 7, y can be 3</p>

<p>7+3 = a) 10</p>

3

<p>^Dam it, I was about to post how to do it!!!</p>

4

<p>Thanks a bunch!</p>

5

<p>"value of x and y"</p>

<p>It should have been written x+y.</p>

6

<p>^ I was going to mention this. Is "x and y" how it's written in the test? Because that's a bit vague.</p>

7

<p>oh sorry it's x+y</p>