Finding (x+y)^2 given x^2 + y^2 = 16 and xy = 8

[Dooga Blackrazor]

A Question

1. If x^2 + y^2 = 16 and xy = 8 then what is (x+y)^2 ?

32, correct?

90?
120?
1260?
150?

 

[arildno]

1. Incorrect; think again.

 

[Dooga Blackrazor]

I meant to put 32, whoops.

 

[arildno]

Still incorrect..

 

[Dooga Blackrazor]

(x+y)^2 = x^2 +2xy + y^2

xy = 8
x^2 + y^2 = 16

2(8) = 16 + 16 = 32

Where am I going wrong?

 

[arildno]

Well, from your first post, it says xy=18..

 

[Dooga Blackrazor]

Ah, thanks.