please help me to solve this question
sec^2A+tan^2A=(1-sin^4A)sec^4A
since sec^2-tan^2=1, you can multiply by that:
(sec^2+tan^2)(sec^2-tan^2)
sec^4-tan^4
but, since tan=sin/cos = sin*sec, that's
sec^4-sin^4*sec^4
(1-sin^4)sec^4
sec^2A+tan^2A=(1-sin^4A)sec^4A
(sec^2+tan^2)(sec^2-tan^2)
sec^4-tan^4
but, since tan=sin/cos = sin*sec, that's
sec^4-sin^4*sec^4
(1-sin^4)sec^4