Prove that :- cos2x = (1 - tan²x)/(1 + tan²x)

cos2x = (1 - tan²x)/(1 + tan²x)
cos2x=1-tan^2x/1+tan^2x
1-tan^2x/1+tan^2x is equal to
Show that cos 2x = 1 - tan^2x/1 + tan^2x.
prove that cos2x=(1-tan^2x)/(1+tan^2x)
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