et a 1 3 1 and z 1 2 3 Write down the dot product 7 7 as a matrix multiplication The solutions of Az 0 are the vectors in R that are perpendicular to the vector raw the row and column pictures for the equations z 3y 4 and x 2y 1 se backward substitution to solve the following two systems of equations 2 1 22 and 21 2 3x3 202 323 6