Question

Himpunan penyelesaian dari
cos (-3x) = cos 27° , -180°≤x≤360°

Answer 1

Cos (-3x) = cos 3x = cos 27
3x = 27 +k. 360 atau 3x = -27 + k.360
x = 9 + k.120 atau x  = -9 + k.120
k = 0,1,2,3,4,5

k=0 --> x = 9, x=  -9
k = 1 --> x = 129, x = 111
k = 2--> x = 249, x = 231
k = 3 --> x = 369 , x = 351
HP =(-9,9 ,111,129,231,249, 351)