xSn=x^2+2x^3+…nx^(n+1) 与Sn=x+2x^2+3x^3+…nx^n相减等于多少

学习时间:2026-08-13 18:48:48 阅读：2351

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2026-08-13 18:48:48

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xSn-Sn=(x^2+2x^3+…nx^(n+1))-(x+2x^2+3x^3+…nx^n)=-x-x^2-x^3-。。-x^n+nx^(n+1)=-x(x^(n+1)-1)/(x-1)+nx^(n+1)

xSn=x^2+2x^3+…nx^(n+1) 与Sn=x+2x^2+3x^3+…nx^n相减 等于多少