2/1*(1+2)+3/(1+2)*(1+2+3)+4/(1+2+3)*(1+2+3+4)+...+(1+2+3+...+99)*(1+2+...+100)是多少,
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![2/1*(1+2)+3/(1+2)*(1+2+3)+4/(1+2+3)*(1+2+3+4)+...+(1+2+3+...+99)*(1+2+...+100)是多少,](/uploads/image/z/9491696-8-6.jpg?t=2%2F1%2A%281%2B2%29%2B3%2F%281%2B2%29%2A%281%2B2%2B3%29%2B4%2F%281%2B2%2B3%29%2A%281%2B2%2B3%2B4%29%2B...%2B%281%2B2%2B3%2B...%2B99%29%2A%281%2B2%2B...%2B100%29%E6%98%AF%E5%A4%9A%E5%B0%91%2C)
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2/1*(1+2)+3/(1+2)*(1+2+3)+4/(1+2+3)*(1+2+3+4)+...+(1+2+3+...+99)*(1+2+...+100)是多少,
2/1*(1+2)+3/(1+2)*(1+2+3)+4/(1+2+3)*(1+2+3+4)+...+(1+2+3+...+99)*(1+2+...+100)是多少,
2/1*(1+2)+3/(1+2)*(1+2+3)+4/(1+2+3)*(1+2+3+4)+...+(1+2+3+...+99)*(1+2+...+100)是多少,
原式=1/1-1/(1+2) + 1/(1+2)-1/(1+2+3) + .+ 1/(1+2+...+99)-1/(1+2+...+100)
消去一些项之后,有:
原式=1/1-1/(1+2+...+100)=1-1/5050=5049/5050