📝 题目
4. 1.1 求下列级数的和:
(1) $\mathop{\sum }\limits_{{n = 1}}^{\infty }\frac{1}{\left( {{3n} - 2}\right) \left( {{3n} + 1}\right) }$ ; (2) $\mathop{\sum }\limits_{{n = 1}}^{\infty }\frac{{\left( -1\right) }^{n - 1}}{n\left( {n + 2}\right) }$ .
💡 答案与解析
4. 1.1 (1) $\frac{1}{3};\;\left( 2\right) \frac{1}{4}$ .