1、az/ax=e^(x+y)+xe^(x+y),az/ay=xe^(x+y),
a^2z/ax^2=2e^(x+y)+xe^(x+y),a^2z/axay=e^(x+y)+xe^(x+y),
a^2z/ay^2=xe^(x+y).
2、交换积分顺序,原积分
＝积分（从0到2）dx 积分（从0到x/2）e^(x^2)dy
＝积分（从0到2）xe^(x^2)dx/2
＝e^(x^2)/4|上限2下限0
＝(e^4－1)/4.
3、当n趋于无穷时,liim a(n+1)/an=lim 3^(n+1)/(n+1)!*n!/3^n
=lim 3/(n+1)＝0