un=x^(4n+1)/(4n+1)un+1=x^(4n+5)/(4n+5)=lim(n->∞)[x^(4n+5)/(4n+5)]/[x^(4n+1)/(4n+1)]=x^4<1即|x|<1收敛|x|>1发散所以收敛半径=1
