equation..tough one

[resilient]

a^2+B^2=2AB=9

how do you deduce down to (A+B)^2=9 I dont see this step

answer is 3 or -3.

[Stuart@KaplanGMAT]

a^2+B^2=2AB=9

how do you deduce down to (A+B)^2=9 I dont see this step

answer is 3 or -3.

It looks like you've completely misstated the equation. Is this even data sufficiency?

Based on what you've posted, I'm going to try to reverse engineer the question. Wish me luck!

Q: what's the value of a+b?

(1) a^2 + b^2 + 2ab = 9

The left side of the equation is a classic quadratic - a perfect square (which is usually written as a^2 + 2ab + b^2). We can simplify the left side to:

(a+b) (a+b) or (a+b)^2

so, we have (a+b)^2 = 9

if we had x^2 = 9, we'd know that x = +3 or -3

(a+b)^2 is the same thing as x^2, so we know that (a+b) = +3 or -3

Since we get 2 values, statement (1) is insufficient.

* * *

Was I close?

In the future, please post the entire question, it makes it much easier for people to help you out.

[resilient]

a^2+B^2+2AB=9 question is A+B=?

how do you deduce down to (A+B)^2=9 I dont see this step

answer is 3 or -3.

[resilient]

thanks to you i see my mistake I just never saw it as a perfect square. awesome