buktikan 1 - cos 2alpha / sin 2alpha = tg alpha

cos 2 alpha = cos(alpha + alpha)
= cos alpha cos alpha - sin alpha sin alpha
= cos^2 alpha - sin^2 alpha
= 2 cos^2 - 1 alpha
= 1 - 2 sin^2 alpha

sin 2 alpha = sin( alpha + alpha)
= sin alpha cos alpha +cos alpha sin alpha
= 2 sin alpha cos alpha

tan alpha = sin alpha / cos alpha