Well, I don't entirely know how to describe this, however I do know that 1-Sin^2(x) is equal to Cos^2(x), and that Tan(7Pi/2) is equal to Tan(Pi/2) so that kinda helps that by reducing to simpler terms Because Cos(a-Pi/2) is also equal to Cos(Pi/2-a). Also, Cos(3Pi/2+a) is equal to -Cos(Pi/2+a). Tan(Pi/2+a) is equal to Sin(Pi/2+a)/Cos(Pi/2+a). I just hope this helps you out, sorry if this doesn't help at all Xd