f(x)=x^2/4+x^3

find the power series representation...so far i found ...Óx^2n+2/4^n...is dat correct?...nd then it is asking to find the radius and interval of convergence...i found the radius to be x^2/4...so i set the radius between -1 and 1...nd then solve for x...i got x to be -2 and 2...so when i plug in -2 and 2 i cant tell if they converge or diverge? how do i do dat?

I don't understand the question
f(x)=x^2/4 +x^3
is already a power series, with only two terms. it converges everywhere.