需要求什么?
a0,a1,a2,a3,a4
如果是：用 Pascal 三角形
(ax+b)^4 = (ax)^4 + 4(ax)^3(b)^1 + 6(ax)^2(b)^2 + 4(ax)^1(b)^3 +(b)^4
所以 a = 2,b = 1
a0 = a^4 = 16
a1 = 4a^3 = 32
a2 = 6a^2 = 24
a3 = 4a^1 = 8
a4 = b^4 = 1