1. The problem statement, all variables and given/known data tan^2x - sin^2x = sin^2x*tan^2x 2. Relevant equations 3. The attempt at a solution This is how my teacher solved it. Sin^2x sin^2x ______ - ______ Cos^2x 1 sin^2x - cos^2x*sin^2x _________________________ cos^2x = sin^2x (1-cos^2x) ___________________ cos^2x =sin^2x *sin^2x ______________ cos^2x thus giving the answer. I dont understand what happends on the third line. How can 1-cos^2x be bracketed if cos^2x*sin^2x are one term, even though they equal one, how can that equal 1-cos^2x?