# Chapter 3.1

## Class 9

### Linear transformations

• If A is an n x m matrix, then $T:R^m->R^n$ defined by $Tx=Ax$ is a linear transformation.

## Class 10

(Midterm @ Class 11)

## Class 12

If you know what T does $u_1, u_2, u_3$, then you can find that T does to any vector in span{$u_1, u_2, u_3$}.

T is not well-defined.