can you plzz solve this question:

1-tan^2A/1+tan^2A=Cos2A

=1-tan²a/1+tan²a

=1 - (sin²a/cos²a) / 1 + sin²a/cos²a

=(cos²a-sin²a) / (cos²a+sin²a)

=cos²a-sin²a/1

=cos2a  (using cos2a=cos²a-sin²a)