Given f(x)=∑anxnf(x) = \sum a_n x^nf(x)=∑anxn with an=2n/n!a_n = 2^n / n!an=2n/n!, what is f(x)f(x)f(x)?
exe^xex
e2xe^{2x}e2x
2ex2e^x2ex
ex/2e^{x/2}ex/2