Given number: x+81 It is a series of species ax(cx−x0)dx - power series. The radius of convergence of a power series can be calculated by the formula: Rd=cx0+limx→∞ax+1ax In this case ax=x+81 and x0=0 , d=0 , c=1 then 1=x→∞lim(x+8x+9) Let's take the limit we find