Buktikan bahwa : cos pangkat 4 x (1-tan pangkat 4 x) = 1-2 sin²x
tinuhn
Cos^4 x*(1-tan^4 x) cos^4 x (1-sin^4 x/cos^4 x) cos^4 x (cos^4 x/cos^4 x - sin^4 x/cos^4 x) cos^4 x (cos^4 x - sin^4 x)/cos^4 x cos^4 x-sin^4 x (cos^2 x - sin^2 x) (cos^2 x + sin^2 x) --->(cos^2 x + sin^2 x = 1) (cos^2 x - sin^2 x) 1 --->(cos^2 x = 1 - sin^2 x) 1 - sin^2 x - sin^2 x 1 - 2 sin^2 x
cos^4 x (1-sin^4 x/cos^4 x)
cos^4 x (cos^4 x/cos^4 x - sin^4 x/cos^4 x)
cos^4 x (cos^4 x - sin^4 x)/cos^4 x
cos^4 x-sin^4 x
(cos^2 x - sin^2 x) (cos^2 x + sin^2 x) --->(cos^2 x + sin^2 x = 1)
(cos^2 x - sin^2 x) 1 --->(cos^2 x = 1 - sin^2 x)
1 - sin^2 x - sin^2 x
1 - 2 sin^2 x