Question

I really need help with this question on multiplying matrices, I've been stuck on it for over 20 minutes and I'm about to cry (ignore the 240 at the end, it's probably wrong)

Answer 1

This is not fun

so
we mutiply the number of rows of the first matrix by the number of collumns of the second matrix

3*2 is the dimentions of the resulting matrix
you have
$\left[\begin{array}{cccc}9&4&8&6\\2&0&3&1\\1&-2&5&0\end{array}\right] \left[\begin{array}{cc}12&2\\15&1\\3&9\\8&11\end{array}\right] =$$\left[\begin{array}{cc}9*12+4*15+8*3+6*8&9*2+4*1+8*9+6*11\\2*12+0*15+3*3+1*8&2*2+0*1+3*9+1*11\\1*12+-2*15+5*3+0*8&1*2+-2*1+5*9+0*11\end{array}\right]$=$\left[\begin{array}{cc}108+60+24+48&18+4+72+66\\24+0+9+8&4+0+27+11\\12+-30+15+0&2+-2+45+0\end{array}\right]$=$\left[\begin{array}{cc}240&160\\41&42\\-3&45\end{array}\right]$