cos (x+7/4π ) - cos (x - 7/4π ) = 1 Untuk 0≤x≤360

jawab

A = x + 7/4 π
B = x - 7/4 π
A+B = 2x
A- B = 7/2 π

cos  A - cos B = 1
- 2 sin 1/2 (A + B) sin 1/2 (A-B) = 1
- 2 sin 1/2 (2x)  sin 1/2 (7/2 π) = 1
- 2sin x  sin 7/4 π = 1
-2 (sin x) (sin 315) = 1
- 2 (sin x)(sin (360 - 45)) = 1
- 2 (sin x)(sin 45) = 1
- 2 (1/2 √2)  sin x = 1
- √2 sin x = 1
sin x = - 1/2 √2

sin x = -1/2 √2 = sin 225 = sin 315
x = {225 , 315}