Buktikan bahwa 1-tan^2 t / 1+tan2 t = 1-2sin^2 t

Jika gini
(1 – tan²t)/(1 + tan²t)
= (1 – (sin²t/cos²x)) / (1 + (sin²t/cos²t))
= ((cos²t – sin²t)/cos²t) / ((cos²t + sin²t)/cos²t)
= (cos²t – sin²t) / (cos²t + sin²t)
cos²t + sin²t = 1, maka
= cos²t – sin²t
cos²t = 1 – sin²t, maka
= 1 – sin²t – sin²t
= 1 – 2 sin²t ← terbukti

ato dg cara lain…