四次方程 : ax4 + bx3 + cx2 + dx + e = 0注意 : 让p和q是任何两个非零数的平方根根. p = sqrt(y1) q = sqrt(y3) r = -g / (8pq) s = b / (4a) x1 = p + q + r - s x2 = p - q - r - s x3 = -p + q - r - s x4 = -p - q + r - s