x的平方 + x - 1/2 = 0
x的平方 + x +1/4 - 1/4- 1/2 = 0
(x+1/2)的平方 - 3/4 = 0
(x+1/2+√3/2)(x+1/2-√3/2) = 0
x1 = -1/2-√3/2
x2 = -1/2+√3/2