The Right Hand Rule b a axb
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 triple a.(bxc) But recall that the components of (bxc) come from 2x2 determinants
a.(bxc) A-ha! We have a quick way to compute this!
The Geometric Interpretation Volume of a parallelpiped V = |bxc| |a||cos( )|=|a.(bxc)| 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)