Bantuan nya.Hitunglah nilai 2cos50° cos40°-2sin95°sin85°?

Misal : A = 50°
B = 40°
C = 95°
D = 85°
2Cosa. Cosb = cos(a+b) + cos(a-b)
-2Sina. Sinb = cos(a+b) - cos(a-b)
2CosA.CosB - 2SinC.SinD =
Cos(A+B) + Cos(A-B) + Cos(C+D) - Cos(C-D)
(Masukkan sudut)

= cos90° + Cos10° + Cos180° - Cos10°
= cos90° + Cos180°
= 0 + (-1)
= -1