Help with squaring geometry help

[PiRsq]

x and y are vectors

If |x|=11 and |y|=23 and |x-y|=30, find |x+y|?

I tried but I couldn't get it, any hints out there guys?

 

[Hurkyl]

Try squaring everything.

 

[PiRsq]

I did

|x|^2 + |y|^2 = |x+y|^2

Then |x+y|=25.6 units

But my book's answer says 16 units...I don't get it

 

[Hurkyl]

That formula only works when x and y are perpendicular vectors.

Recall that for any vector z:

|z|^2 = z * z

So what should |x + y|^2 and |x - y|^2 be?

 

[PiRsq]

Thanks man