Answer:
B
Step-by-step explanation:
This is a quadratic in cosines
Factor by considering the factors of the product 2 × 1 = 2 which sum to give the coefficient of the cos x term (3 )
the factors are + 2 and + 1
use these factors to split the middle term
2cos²x + 2cosx + cosx + 1 = 0 (factor by grouping )
2cosx(cosx + 1) + 1(cosx + 1) = 0 (take out common factor (cosx + 1) )
(cosx + 1)(2cosx + 1) = 0
equate each factor to zero and solve for x
cosx + 1 = 0
cosx = - 1 ⇒ x = π
2cosx + 1 = 0
cosx = -
since cosx < 0 then x is in second/ third quadrant
x = or x =