Cual es el valor del angulo en la siguiente ecuacion :sinx - sin x / 2 = 0 : ´)?

Se sabe que <img src="https://tex.z-dn.net/?f=Sen%5C%2C%5Cfrac%7B%5Ctheta%7D%7B2%7D%3D%5Csqrt%7B%5Cfrac%7B1-Cos%5C%2C%5Ctheta%7D%7B2%7D%7D" />Entonces : <img src="https://tex.z-dn.net/?f=Sen%5C%2Cx-Sen%5C%2C%5Cfrac%7Bx%7D%7B2%7D%3D0%5C%5C%5C%5CSen%5C%2Cx-%5Csqrt%7B%5Cfrac%7B1-Cos%5C%2Cx%7D%7B2%7D%7D%3D0%5C%5C%5C%5CSen%5E2x%3D%5Cfrac%7B1-Cos%5C%2Cx%7D%7B2%7D%5C%5C%5C%5C2%5C%2C%281-Cos%5E2x%29%3D1-Cos%5C%2Cx%5C%5C2-2%5C%2CCos%5E2x-1%2BCos%5C%2Cx%3D0%5C%5C1-2%5C%2CCos%5E2x%2BCos%5C%2Cx%3D0" />que con <img src="https://tex.z-dn.net/?f=Cos%5C%2Cx%3Du" /> es una ecuacion cuadratica general <img src="https://tex.z-dn.net/?f=1-2u%5E2%2Bu%3D0%5C%5C%5C%5Cu%3D%5Cfrac%7B-1%5Cpm%5Csqrt%7B1%5E2-4%28-2%29%281%29%7D%7D%7B2%28-2%29%7D%3D%5Cfrac%7B-1%5Cpm3%7D%7B-4%7D%3D%5C%7B1%2C-%5Cfrac%7B1%7D%7B2%7D%5C%7D" />o sea : <img src="https://tex.z-dn.net/?f=u%3D%5C%7B1%2C-%5Cfrac%7B1%7D%7B2%7D%5C%7D%3DCos%5C%2Cx%5C%5C%5C%5Cx%3D%5CBig%5C%7BArcCos%5C%2C%281%29%2CArcCos%5C%2C%28-%5Cfrac%7B1%7D%7B2%7D%29%5CBig%5C%7D%5C%5C%5C%5Cx%3D%5C%7B0%2C%5Cpm%20%5Cfrac%7B2%5Cpi%7D%7B3%7D%5C%7D%5Cqquad%20%5Ctext%7B%28angulos%20son%20radianes%29%7D" />.