Help with squaring geometry help

  • Thread starter PiRsq
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  • #1
PiRsq
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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?
 

Answers and Replies

  • #2
Hurkyl
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Try squaring everything.
 
  • #3
PiRsq
112
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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
 
  • #4
Hurkyl
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Science Advisor
Gold Member
14,967
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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?
 
  • #5
PiRsq
112
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Thanks man
 

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