i never learned those formulas.. or maybe we're not there yet?? i don't know.
so..
(cot^2 x -1)/(cot^2 x +1)= 1-2sin^2 x
[(cos^2 x/ sin^2 x) -1] / [(cos^2 x/sin^2 x) +1]
[(cos^2x*sin^2 x/sin^4 x) -1]/[(cos^2x*sin^2 x/sin^4 x) +1]
?
then.. i don't know. i'll just ask my teacher, maybe she has some way to do it using methods i have already learned.
If you're given questions like the one you posted then you're expected to know the things I mentioned in my previous post. The application of these things in a particular question is what you can be helped with. But if you don't know these things, then you need to go back to your class notes and textbook and review that material so that you do know them.