Question

Sec4 x - tan4 x = sec2 x + tan2 x

Answer 1

Sec^4 x - tan^4 x = sec^2 x + tan^2 x
(sec^2 x + tan^2 x) (sec^2 x - tan^2 x) = sec^2 x + tan^2 x)
Ingat: tan^2 x +1 = sec^2 x --> 1 = sec^2 x - tan^2 x
(sec^2 x + tan^2 x) 1 = sec^2 x + tan^2 x
sec^2 x + tan^2 x = sec^2 x + tan^2 x
[Q.E.D]