判断正项级数敛散性，求详细过程啊谢谢大佬们! 80
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思路：考察（1-x)^(-2/3)的二项展开
（1-x)^(-2/3) = 1 + (2/3)x + (-2/3)(-2/3-1)/2! x^2 + ...
= 1 + (2/3) x + (2/3)(5/6) x^2 + ...+ [(2*5*8*...(3n-1)/(3*6*9*...(3n)] x^n
当 x->1-时，得 1 + (2/3) + (2/3)(5/6) + ...+ [(2*5*8*...(3n-1)/(3*6*9*...(3n)] -> oo
（1-x)^(-2/3) = 1 + (2/3)x + (-2/3)(-2/3-1)/2! x^2 + ...
= 1 + (2/3) x + (2/3)(5/6) x^2 + ...+ [(2*5*8*...(3n-1)/(3*6*9*...(3n)] x^n
当 x->1-时，得 1 + (2/3) + (2/3)(5/6) + ...+ [(2*5*8*...(3n-1)/(3*6*9*...(3n)] -> oo
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