jika sin x = p, maka cos2x =

(sin x - cos x)² = p²
sin²x + cos²x - 2 sin x cos x = p²
1 - sin 2x = p²
sin 2x = 1 - p²

semoga membantu :-)

cos2x = 1-2sin²x
cos2x = 1-(sin²x+sin²x)
karena sinx = p maka:
cos2x = 1-(p²+p²)
cos2x = 1-2p²

semoga membantu