(1)
f'(x) = 3x^2 + 2bx + c
图像关于直线x=2对称 -> -(2b)/6 = 2,b = -6.
(2)
f'(x) = 3x^2 - 12x + c,
这个函数单增单减再单增,
t = ( 12 + 根号(144 - 12c) )/6 属于(2,+infinity)
36 - 6c = (3t - 6)^2
c = 6t - 3/2 t^2
f(x)=t^3-6t^2+t(6t - 3/2 t^2)
= t^3-6t^2+6t^2 - 3/2 t^3
= -1/2 t^3 属于(-infinity,-1/4).