1x2+2x3+3x4…+10x11 1x2x3+2x3x4+3x4x5+…7x8x9写

小扁Kid2022-10-04 11:39:541条回答

1x2+2x3+3x4…+10x11 1x2x3+2x3x4+3x4x5+…7x8x9写
1x2+2x3+3x4…+10x111x2x3+2x3x4+3x4x5+…7x8x9写出过程

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schg010 共回答了17个问题 | 采纳率88.2%: 1x2+2x3+3x4+…+n(n+1)
=1x(1+1)+2x(2+1)+3x(3+1)+…n(n+1)
=(1^2+2^2+3^2+…+n^2)+(1+2+3+…+n)
=n(n+1)(2n+1)/6+n(n+1)/2
=n(n+1)[(2n+1)+3]/6
1x2+2x3+3x4+…+10x11
=10x(10+1)x[(10x2+1)+3]/6
=110x4
=440; 1年前