Here I’ll show how to find the matrix of a linear transformation by doing so for the transformation corresponding to the differentiation of a second-degree polynomial. This transformation takes the coefficients of the polynomial to be differentiated and returns the coefficients of the derivative, which is a first-degree polynomial. We know that
and so we have
the matrix of is 2-by-3. (The product of two matrices has as many rows as the first matrix, and as many columns as the second matrix. Also, two matrices can be multiplied only if the first matrix has as many columns as the second one has rows.) Thus,
for some through . We can see that
It is clear that , , and the remaining ’s are 0. This gives us
with the transformation matrix being
As a closing note, we could just as well have be a mapping from to , in which case the transformation matrix would be 3-by-3, and one of its rows would contain only zeros.