Thread: Proving a Trig Identity

Hi there, I need help proving a trig ident. steps plz,

cos2x= (1-tan^2(x))
..........(1+tan^2(x))

tan^2(x) is tan(x)^2....if u don't understand my writing

Please, any help is appreciated, thanks

You can use the identity:



It'll fall into place.

thanks so much

Originally Posted by compuwiz

cos2x= (1-tan^2(x))
..........(1+tan^2(x))

(Basic identity.)

Now split the original fraction into two sums:



And this is exactly equal to double-angle cosine formula.