Physics Help Forum How should I prove this?

 Kinematics and Dynamics Kinematics and Dynamics Physics Help Forum

 Oct 14th 2010, 02:48 PM #1 Junior Member   Join Date: Oct 2010 Posts: 2 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!
 Oct 14th 2010, 03:55 PM #2 Senior Member   Join Date: Mar 2010 Location: Lithuania Posts: 105 Please read vectors dot product help Dot product - Wikipedia, the free encyclopedia
 Oct 14th 2010, 04:38 PM #3 Junior Member   Join Date: Oct 2010 Posts: 2 So then would I start off by doing: |a| = a = sqrt(a_x^2 + a_y^2)? I am still pretty lost
 Oct 15th 2010, 02:20 PM #4 Senior Member   Join Date: Mar 2010 Location: Lithuania Posts: 105 Using properties of dot product (a+b) (c+d)=a(c+d)+b(c+d)=ac+ad+bc+bd

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