Math 2890 Sample Exam Problems

Rows of matrix products

Let $A=\left(\begin{array}{rrrrr} 7 & 5 & 9 & 4 & 4 \\ 8 & 0 & -9 & 8 & 3 \\ -5 & -5 & 3 & 6 & -3 \\ 9 & 2 & -8 & -9 & -5 \end{array}\right)$ and $B = \left(\begin{array}{rrrrr} 0 & -9 & -1 & 7 & 1 \\ 2 & 8 & -7 & -4 & 5 \\ 3 & 6 & -5 & -7 & -4 \\ -4 & 8 & 4 & -4 & -3 \\ 8 & 7 & 6 & 0 & 9 \end{array}\right)$.

Compute row 4 of `AB` by first writing it as a linear combination of the rows of `B`.