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The Right Hand Rule. axb. b. a. Properties of the Cross Product . a x b = - b x a (c a )x b = c( a x b ) = a x(c b ) a x( b + c ) = a x b + a x c ( a + b )x c = a x c + b x c a . ( b x c ) = ( a x b ) . c a x( b x c ) = ( a . c ) b -( a . b ) c.
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The Right Hand Rule axb b a
Properties of the Cross Product • axb = -bxa • (ca)xb = c(axb) = ax(cb) • ax(b+c) = axb + axc • (a+b)xc = axc + bxc • a.(bxc) = (axb).c • ax(bxc) =(a.c)b-(a.b)c
The so-called scalar triplea.(bxc) But recall that the components of (bxc) come from 2x2 determinants
a.(bxc) A-ha! We have a quick way to compute this!
V = |bxc| |a||cos( )|=|a.(bxc)| The Geometric InterpretationVolume of a parallelpiped bxc a h c b Volume = (Area of Base)*(height)
Q. How can we use the cross product to determine if 3 vectors are coplanar (lie in the same plane)? • Determine if the volume of the • resulting parallelpiped is nonzero
Example Do the following points lie in the same plane? A=(1,-1,2) B=(2,0,1) C=(3,2,0) D=(5,4,2)