Sam reviewed how to multiply matrices. She discovered that Matrix Multiplication is not commutative. She learned that multiplying by the Identity Matrix keeps the Identity of the Matrix. We looked at how to place the vertices of a polygon in a matrix. Such a matrix will always have 2 rows - the first row is the x-coordinate of a point, the second row is the y-coordinate. There are four different matrices, each containing zeros, 1, and -1, that we can use to multiply by a matrix and produce a transformation. These transformations are reflections across the x-axis, y-axis, y=x, or y=-x. Samantha worked through several examples of each type of matrix operation.