Finding the value of x for which the power series converges.
For what values of Z does the power series
1 - 3x + (5x2/2!) - (7x3/3!) + (9x4/4!) - (11x5/5!) + ...
Converge? If it converges on an interval of values of x, you do not need to determine whether or not it converges at the endpoints of that interval.