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Old Oct 14th 2010, 02:48 PM   #1
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How should I prove this?

How can I prove this?

The following are all vectors:
a, b, c, d

k = (a+b) (c+d)

prove: k = (a x c) + (a x d) + (b x c) + (b x d)


Any help would be appreciated. Thanks!
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Old Oct 14th 2010, 03:55 PM   #2
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Please read vectors dot product help
Dot product - Wikipedia, the free encyclopedia
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Old Oct 14th 2010, 04:38 PM   #3
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So then would I start off by doing:

|a| = a = sqrt(a_x^2 + a_y^2)?

I am still pretty lost
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Old Oct 15th 2010, 02:20 PM   #4
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Using properties of dot product
(a+b) (c+d)=a(c+d)+b(c+d)=ac+ad+bc+bd
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