Question

∑的上面为∞下面为(n=1),∑(-1)^n*((x^n)/(n^2))的熟练半径和收敛区间

Answer 1

lim(n→∞)|{(-1)^(n+1)[x^(n+1)/(n+1)²]}/{(-1)^n[(x^n)/n²]}|

=lim(n→∞)|xn²/(n+1)²|

=|x|