the weierstrass theorem （维尔斯特拉斯定理

the weierstrass theorem （维尔斯特拉斯定理
(1) draw diagram of cases in which a feasible set (budget set) is not closed or not bunded,but a solution to the optimization problem exists.
(绘制图的情况下,其中一个可行集（预算集）不闭合或不堤壆,但存在的最优化问题的解决方案)
(2)show f(x)=1,g(x)=x are continuous functions.
显示函数f（x）= 1,G（X）=x是连续函数
(3)Does the following function has a maximum on the inverval [-1,1]?If not,explan why.
请问以下函数有一个最大的区间[-1,1]?如果没有,请解释原因.
f(x)= 1/x,x=/=0；
0,x=0.