This problem is a checkpoint for operations with matrices.  

Let $A = \left[ \begin{array} { r r } { - 4 } & { 8 } \\ { - 1 } & { - 12 } \end{array} \right]$, $B = \left[ \begin{array} { c c c } { - 9 } & { 0 } & { 10 } \\ { - 10 } & { 3 } & { - 8 } \end{array} \right]$, $C = \left[ \begin{array} { r r } { - 8 } & { 0 } \\ { 0 } & { - 5 } \\ { - 8 } & { - 11 } \end{array} \right]$, and $D = \left[ \begin{array} { c c c } { 2 } & { 1 } & { 6 } \\ { - 7 } & { - 8 } & { - 11 } \end{array} \right]$. Compute each of the following matrices or values, if possible.

Check your answers by referring to the selected answers.

Ideally at this point you are comfortable working with these types of problems and can complete them correctly. If you feel that you need more confidence when completing these types of problems, then review the Operations with Matrices Checkpoint materials available at cpm.org and try the practice problems provided. From this point on, you will be expected to do problems like these correctly and with confidence.