1+3+6+10+15+21+28+36,请写∑ notation,

来源：学生作业帮编辑：作业帮分类：数学作业时间：2024/07/05 08:24:30

1+3+6+10+15+21+28+36
=1/2*1*2+1/2*2*3+1/2*3*4+...+1/2*8*9
=1/2[1*2+2*3+3*4+...+8*9]
=1/2[1/3*1*2*3+1/3*(2*3*4-1*2*3)+1/3(3*4*5-2*3*4)+...+1/3(8*9*10-7*8*9)]
=1/6(1*2*3+2*3*4-1*2*3+3*4*5-2*3*4+...+8*9*10-7*8*9)
=1/6*8*9*10
=120
公式：1*2+2*3+3*4+...+n(n+1)=1/3n(n+1)(n+2)

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