工程數學之求收斂發散半徑（１）

Q3: By ratio test
|a(m+1)/a(m)|= | (2m+1)(2m+2)*m^2/(m+1)^2 x |
lim(m->∞) | a(m+1)/a(m)| =
{0, x=0
{∞, x ≠0
so, the radius of this infinite series is 0 (converges only for x=0)

Q4:By root test
| a(m) |^(1/m) = | mx | ->
{ 0, x=0
{infty x≠0
so, the radius of the infinite series is 0 (converges only for x=0)