f(x)=(x-1)e^x
=(x-1)e^(x-1)*e
=e*(x-1)e^(x-1)
e^(x-1)=∑(n=0,+∞) (x-1)^n/n!
所以
f(x)=e*(x-1)*∑(n=0,+∞) (x-1)^n/n!
=e*∑(n=0,+∞) (x-1)^(n+1)/n!