Question

simplify sec X -sec X sin^2 X

Answer 1

http://www.wolframalpha.com/input/?i=++sec+X+-sec+X+sin%5E2+X

Answer 2

write out your expand your sin^2 term to (sin)(sin).
sec = (sec)(sin)(sin)
use the trig identity sec=1/cos on the second sec in your equation
sec = (sin)(sin)/cos
use the trig identy tan=sin/cos
sec=(tan)(sin)