Matrix Operations: Show A^2 = [[cos20 -sin20][sin20 cos0]]

[maeveoneill]

Let A=
[cos0 -sin0 ] *0= theta
[sin0 cos 0]

Show that A^2 =
[cos 20 -sin20]
[ sin 20 cos0]

When I figure out A^2 I get:
[cos 20 -sin20 cos0- sin 0 + cos0-sin0]
[sin0cos0 +sin0 cos0 -sin20 +cos 0 ]

How do I end up with
[cos 20 -sin20]
[ sin 20 cos0] instead?