Hi, i need help in the following question:

I need to prove that there are a_0, a_1,... in R and r>0 such that the series ∑(a_n)x^n converge when |x|< r, and such that ∑(a_n)x^n = arctanx for every |x|< r

What should i do here? Use the Taylor series of arctanx or something?

Thanks for any help, and sorry for the mess :)