求幂级数的收敛半径和收敛区间．
参考答案：
解析：当x=5时级数成为收敛，当x=-5时，级数成为收敛，所以幂级数的收敛区间为[-5，5]
—What a hard life my parents live!
—So do my parents.When I grow up, I ______ to make them live more happily. [ ]
A. try
B. tried
C. will try
D. have tried
6σ的核心概念有客户、（）、现有能力、应有能力、缺点、变异。
