simplify
options for the answer are:
cos^2 θ
-sin^2 θ
-cos^2 θ
sin^2 θ
I;m using x instead of theta (it doesn't matter )
Note that sin (-x) = - sin (x) and sec (-x ) = sec (x)
sin (-x) tan (x) - sin (x) sin x / cos x - sin^2 x
___________ = __________________ = ____________ = - sin^2 x
sec (-x) sec (x) (1/cos x) cos x
