This should be clear after you convert to sines and cosines.

Factor out a What is (Know your identities!)2. (cos^2x)(sin^2x)-(sin^2x)

Convert to cosines, get a common denominator in the second factor, and simplify. (Again, you will need to make use of an important identity)3. secx(secx - cosx)

Convert to sines and cosines, and then reduce.4. (cos^2x)(tanx)/(sinx)