Question

2sin^2x+sinx=0

Answer 1

Let θ = 2x.

Look at the unit circle and you can see that sinθ = ½ for θ = π/6, 5π/6 radians.
x = π/12, 5π/12 radians
= 15°, 75°

Answer 2

just thinking logically, can the square of a number be a negative value ??