(2-3*5^-1)+(4-3*5^-2)+...+(2n-3*5^-n)
=2+4+6+8+……+2n-3(5^-1+5^-2+5^-3+……+5^-n)
=n^2+n-3*(1/5)*(1-(1/5)^n)/(1-1/5)
=n^2+n-3/4+3/4*(1/5)^n
用分组法求和求Sn=(2-3*5^-1)+(4-3*5^-2)+...+(2n-3*5^-n)
用分组法求和求Sn=(2-3*5^-1)+(4-3*5^-2)+...+(2n-3*5^-n)
其他人气:568 ℃时间:2020-04-01 18:31:43
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