Given number: k+7 It is a series of species ak(cx−x0)dk - power series. The radius of convergence of a power series can be calculated by the formula: Rd=cx0+limk→∞ak+1ak In this case ak=k+7 and x0=0 , d=0 , c=1 then 1=k→∞lim(k+8k+7) Let's take the limit we find