<p>20) if a > 0, x^2 + y^2 = a,abd xy = a - 10, what is (x + y)^2 in terms of A?</p>

<p>A)a - 20;

B)2a - 20;

C)2a - 10

D)3a - 20;

E)3a - 10;</p>

<p>Okay I first lets expanded (x + y)^2 , so first step should be this:</p>

<p>x^2 + 2xy + y^2;</p>

<p>We already know xy = a - 10;</p>

<p>x^2 + 2(a - 10) + y^2;

x^2 + 2a - 20 + y^2;</p>

<p>We know that a = x^2 + y^2,so we have have this -></p>

<p>x^2 + 2(x^2 + y^2) - 20 + y^2 -></p>

<p>x^2 + 2x^2 + 2y^2 - 20 + y^2 ->

3x^ + 3y^2 - 20;</p>

<p>Then I expanded the answer to see which one matches this and I got answer as D;</p>

<p>3(a) - 20 -></p>

<p>3(x^2 + y^2) - 20 -> 3x^2 + 3y^2 - 20;</p>

<p>I was able to solve this question only because I had some time left of my section time is there faster way to solve it ?</p>