①f(x1+x2)=f(x1)•f(x2)②f(x1•x2)=f(x1)+f(x2)
③ ④
当 时,上述结论中正确的序号是.
x
1
2
3
f(x)
g(x)
则当 f[g(x)]=2 时, x= {#blank#}1{#/blank#}.