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PiRsq
Sep17-03, 07:00 PM
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
Sep17-03, 07:29 PM
Try squaring everything.

PiRsq
Sep17-03, 08:07 PM
I did

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

Then |x+y|=25.6 units

But my book's answer says 16 units...I dont get it

Hurkyl
Sep17-03, 09:09 PM
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
Sep18-03, 05:07 PM
Thanks man