Question

Am I right?

Answer 1

Sin(90) = 1, sin(180) = 0. When sin(x) = 0, then cos(x) = 1

According to the picture, cos(90*) = 1, though if you work cos(90*) out, it can be seen that cos(90*) = 0

Answer 2

yep. good job
cos(x) = 1 when x=0
sin(x) = 0 when x=0