Cos55 cos40 – sin 55 sin40=….

Cos 40 = p
samping = p
miring = 1

depan = √(1² – p²)
= √(1 – p²)

sin 40 = √(1 – p²)

sin 95 cos 55 = 1/2(sin(95+55) + sin(95-55))
= 1/2(sin150 + sin40)
= 1/2(1/2 + √(1 – p²))
= 1/4 + 1/2 √(1 – p²)

Kmu lgi apa dek