You can put this solution on YOUR website! multiply numerator and denominator by 1 + sin(x)
you get:
cos^2(x) * (1 + sin(x) divided by:
(1 - sin(x)) * (1 + sin(x))
this comes out to be:
cos^2(x) * (1 + sin(x) divided by:
(1 - sin^2(x))
since 1 - sin^2(x) = cos^2(x), then you get:
cos^2(x) * (1 + sin(x) divided by:
cos^2(x) which turns out to be:
1 + sin(x)
see the attached picture for hand drawn calculations:
