Question

Buktikan bahwa cos^4alfa(1-tan^4alfa) = cos^2alfa - sin^2alfa - 1

Answer 1

Cos^4 a(1-tan^4 a)
=cos^4 a(1- (sin^4a/cos^4 a)
=cos^4 a -sin^4 a
=(cos^2 a-sin^2 a)(cos^2a+sin^2 a)
=(cos^2 a- sin^2 a).1