Question

Jika 2sin²x + 3cosx = 0 dan 0° ≤ x ≤ 180° , maka nilai x adalah...

Answer 1

1-sin²x = cos²x

2sin²x + 3cosx = 0
2(1-cos²x) + 3 cosx = 0
2- 2 cos²x + 3 cosx = 0
2cos²x - 3 cos x - 2 = 0
(2cosx +1) ( cosx -2) = 0

2 cos x = -1                  
   cos x = -1/2                     
           x= 120°