由题意,x1+x2 - (x3+x4) = 6
x1+x2 = -b
x3+x4 = -b^2
则 b^2 - b - 6 = 0
b = -2 或 3
x1-x2 = x4-x3
则 |x1-x2| = |x3-x4|
2 sqrt(b^2 - 4c) /2 = 2 sqrt(b^4 - 80) /2
所以 b^4 - b^2 + 4c - 80 = 0
同时
b^2 - 4c >= 0
b^4 - 80 >= 0
此时b一定等于3 而不是-2,因为(-2)^4 - 80 < 0
所以 c = 2
函数为：y = x^2 + 3x + 2
顶点坐标为：( -1.5 ,-0.25 )