Solution 3c 9

Prove 3.52. That if $A$ is an $m$ -by- $n$ matrix and $c$ is an $n$ -by- $1$ matrix.
Then

Ac = c_1A_{\cdot,1} + \dots + c_nA_{\cdot,n}

In other words, $Ac$ is a linear combination of the columns of $A$ , with the scalars that multiply the columns coming from $c$ .

TODO