Okay, so, start by rearranging the problem (because it’s multiplication, you can do that), you get
(sin^2(x)-cos^2(x))*cos(x)*sec(x) + cos^2(x)
cos and sec are inverses, so they cancel each other out leaving you with
sin^2(x)-cos^2(x)+cos^2(x)
The cos^2(x) cancel each other out leaving you with
sin^2(x)
