Diketahui cos x = 3/5. dengan 0° < x < 90° sin 3x + sin x = ...

cos x= 3/5, sin x= 4/5
Maka, sin 3x + sin x adalah....

Jawab:
sin 3x + sin x:
= [3 sin x - 4 sin³ x] + sin x
= [ 3 [4/5] - 4 [sin x]³] + 4/5
= [12/5 - 4[4/5]³] + 4/5
= [12/5 - 4[64/125] + 4/5
= [12/5 - 256/125] + 4/5
= [300/125 - 256/125] + 4/5
= 44/125 + 4/5
= 44/125 + 100/125
= 144/125