jika x1 dan x2 memenuhi persamaan

12 sin² x + sin x - 1 = 0
12 sin² x + 4 sin x - 3 sin x - 1 = 0
4 sin x (3 sin x + 1) - 1 (3 sin x + 1) = 0
(3 sin x + 1) (4 sin x - 1) = 0

1) 3 sin x + 1 = 0
=> 3 sin x = -1
=> sin x = -1/3
=> cosec x = -3/1

2) 4 sin x - 1 = 0
=> 4 sin x = 1
=> sin x = 1/4
=> cosec x = 4/1

cosec² x1 + cosec² x2 - 7
= (-3)² + (4)² - 7
= 9 + 16 - 7
= 18