Question 166219
Multiply rows of the first matrix by columns of the second matrix to get the product. 
Example: First entry of the product matrix, {{{P[1,1]}}},
{{{P[1,1]=2(1)+(-1)(-3)+0(-1)=2+3+0=5}}}
{{{P[1,2]=2(-1)+(-1)(-2)+0(1)=-2+2+0=0}}}
{{{P[1,3]=2(2)+(-1)(4)+0(1)=4-4+0=0}}}
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{{{(matrix(3,3,2,-1, 0,
-1, 1, -2,
1, 0, -1 ))*(matrix(3,3, 
1, -1, 2,
-3, -2, 4,
-1, 1, 1 ))=(matrix(3,3,
5,0,0,
-2,-3,0,
2,-2,1))}}}