Math Problem Help

Test Preparation SAT Preparation
1

<p>If (x+y)^2 - (x-y)^2=84 and x and y are positive integers, which of the following could be the value of x+y ?</p>

<p>A) 10
B) 12
C) 14
D) 16
E) 18</p>

<p>Thanks, btw this is from an old psat prac test.</p>

2

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

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

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

<p>2xy + 2xy + 84</p>

<p>xy = 21</p>

<p>3 times 7 = 21</p>

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

<p>Hope that helps :)</p>