Question

sec^4a-tan^4a=1+2 tan^2a-sec^2A

Answer 1

sec^4A - tan^4A

(sec^2A)^2 - (tan^2A)^2

(sec^2A + tan^2A) (sec^2A - tan^2A)

because (a^2 - b^2) = (a + b) (a - b)

so, (sec^A + tan^2A).1

(1 + tan^2A + tan^2A)

(1 + 2tan^2A).