Answer:
x = π/2 + nπ or x = (2/3 π + 2nπ) or x = (4/3 π + 2nπ)
Step-by-step explanation:
1 + cosx + cos2x=0
1+cosx+(2cos²x -1) = cosx + 2cos²x = cosx (1 + 2cosx) = 0
cosx = 0
x = 90° (π/2) or (90+180) or (90+180x2) .... i.e π/2 + nπ
or 1 + 2cosx = 0
cosx = -1/2
x = 120° or 240° (2/3 π or 4/3 π) or (120 + 360 : 2/3 π + 2π) (120 + 2 * 360)
.... i.e. (2/3 π + 2nπ)
or (240 + 360 : 4/3 π + 2π) (240 + 2 * 360) .... i.e. (4/3 π + 2nπ)
