a_nx^n, b_nx^n are two power series with radius of convergence R1, R2, respectively.

If R1 is different than R2, how can i prove that the radius of convergence of the power series (a_n + b_n)x^n is min{R1, R2}?

And what can be said about the radius of cenvergence if R1=R2?

Thanks for any help :)