Answer:
θ = 90°, 180°, or 270°
Step-by-step explanation:
sin²θ = 1 + cos θ
Use Pythagorean identity.
1 − cos²θ = 1 + cos θ
Move everything to one side and simplify.
0 = cos²θ + cos θ
Factor.
0 = cos θ (cos θ + 1)
Solve.
cos θ = 0 or -1
θ = 90°, 180°, or 270°
