Try it on paper first. A hint, the key idea and the worked solution are here when you need them.
A graphics program reflects every point in the -axis, using the matrix . Then it turns the picture anticlockwise, using the matrix .
Find the single matrix that does both moves in that order, and the final position of the point .
$.
is row of multiplied by column of , and exists when the columns of equal the rows of . Matrix multiplication is associative and distributive but not commutative. The entry of counts routes with steps.
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. The order. acts first, then . So .
Step 2. The product. Row of with column of gives . Row of with column of gives . The other two entries are .
Step 3. The point. $M
=
$.
Step 4. Check the other way. Reflecting first gives . Turning that by anticlockwise gives .
Answer: $M =
y = x(2, 3)$.
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