1.(1)级数发散,因为部分和不收敛
(2)级数收敛,部分和sn=(1/1*3)+(1/3*5)+(1/5*7)+.+(1/(2n-1)(2n+1))=(1/2)[1-(1/3)]+
(1/2)[(1/3)-(1/5)]+(1/2)[(1/5)-(1/7)]+.+(1/2)[(1/2n-1)-(2n+1)]=(1/2)[1-(1/2n+1]=1/2(当n趋于无穷大时)
2.(1)级数收敛 sn=[(-5/6)x(1-(5/6)^n)]/(1/6)=-5
(2)级数发散 ,用柯西判别法可证
(3)级数收敛,将级数拆开来分成两部分考虑