00:01
So we want to figure out what the standard matrix is for a linear transformation that first reflects the vector through the horizontal or the vertical axis and then rotated 90 degrees counterclockwise or pi over two ratings.
00:31
So let's try to construct the matrix.
00:34
So we know that the standard matrix t is given by the columns of t of e1 and t of e2.
00:48
So e1 is the vector 1 -0 and e2.
00:52
And e2 is the vector 01.
00:56
So let's try to see what t does to these two vectors.
01:03
So first, let's draw our vector e1.
01:10
So here's our vector e1.
01:15
So this is the x2 axis, and this is the x1 axis.
01:19
So first we need to reflect it through the x2 axis.
01:28
So if we reflect it over the vertical axis, it's going to become this one in blue.
01:36
And then we need to rotate it 90 degrees counterclockwise.
01:43
So we're going to rotate it, and it's going to be this vector here.
01:50
So nothing we did has changed the length of the vector.
01:52
We've just flipped it and turned it and did these transformations.
01:57
So this is going to be the point negative 1...