急救：mathematica 一元函数求极值

急救：mathematica 一元函数求极值
急救,急救,我有一个关于一元函数求极值的题目,要是解答不出来我就完了.
题目是这样的：一元函数求极值的问题：请设计一个程序包求一元函数在[a,b]上最大值和最小值.要求运行时只要用户任意输入一个一元函数和连续区间[a,b],就计算并告知用户该函数在[a,b]上取最大值和最小值的点和相应的最大值和最小值.
我的程序是：BeginPackage["jizhi`"]
jizhi::uasage = "jizhi is a programme for making MAX and MIN in a hanshu if \
user input a f(x) and geting a exact (x,f(x))"
Begin["`Private`"]
Module[{a,b,x},
f[x_] := Input[ Inputhanshu];
a = Input[please Input zuoduandian];
b = Input[please Input youduandian];
zhudian = Solve[f[x] == 0,x];
zhudianbiao = Union[{x,f[x]} /.zhudian,{{a,f(a)},{b,f(b)}}];
fmax = Max[Transpose[zhudianbiao][[2]]];
fmin = Min[Transpose[zhudianbiao][[2]]];
x1 = Position[zhudianbiao,fmin];
x2 = Position[zhudianbiao,fmax];
Min = zhudianbiao[[x1[[1,1]]]];
Max = zhudianbiao[[x2[[1,1]]]];]
End[]
EndPackage[]
请指点下为什么运行不对呢?
若解答正确,小女子感恩不尽.
非常感谢你能抽时间帮我看，但是我用你修改的程序运行了一遍，还是不对啊？
你修改后的程序是
BeginPackage["jizhi`"]
jizhi::uasage = "jizhi is a programme for making MAX and MIN in a hanshu if \
user input a f(x) and geting a exact (x,f(x))"
Begin["`Private`"]
Module[{a,b,x},f = Input[Inputhanshu];
fff[x_] := f
a = Input[please Input zuoduandian];
b = Input[please Input youduandian];
zhudian = Solve[fff[x] == 0,x];
zhudianbiao = Union[{x,fff[x]} /.zhudian,{{a,fff[a]},{b,fff[b]}}];
fmax = Max[Transpose[zhudianbiao][[2]]];
fmin = Min[Transpose[zhudianbiao][[2]]];
x1 = Position[zhudianbiao,fmin];
x2 = Position[zhudianbiao,fmax];
Min1 = zhudianbiao[[x1[[1,1]]]];
Max1 = zhudianbiao[[x2[[1,1]]]];
{Min1,Max1}]
End[]
EndPackage[]
再帮我看看吧~我用的是4。0