# Matrix Multipication

## Homework Statement

I look at the following:

$$(x_1\,\,x_2)\begin{pmatrix}1&2\\2&4\end{pmatrix}\binom {x_1}{x_2}=(x_1\,\,x_2)\binom {x_1+2x_2}{2x_1+4x_2}=x_1^2+2x_1x_2+2x_1x_2+4x_2^2$$

And I don't understand how they got from $$(x_1\,\,x_2)\binom {x_1+2x_2}{2x_1+4x_2}$$ to $$x_1^2+2x_1x_2+2x_1x_2+4x_2^2$$.

## The Attempt at a Solution

What process is used here? It surely is not matrix multiplication, otherwise the result would have to be a 1x2 matrix.

tiny-tim