Question

How do you verify `(1-tan^2)/(1+tan^2)=cos^2 - sin^2`?

Answer 1

`(1 - tan^2)/(1 + tan^2) = (cos^2 - sin^2)/(cos^2 + sin^2) (cos^2/cos^2)` =

=`(cos^2 - sin^2)/1 = cos^2 - sin^2`