那1×2+2×3+3×4+……+100×101=?,
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那1×2+2×3+3×4+……+100×101=?,
那1×2+2×3+3×4+……+100×101=?,
那1×2+2×3+3×4+……+100×101=?,
1×2+2×3+3×4+……+n×(n+1)
=1^2+2^2+...n^2+1+2+3+...+n=1/6n(n+1)(2n+1)+1/2n(n+1)=1/3n(n+1)(n+2),中间用了两条公式.
取n=100得到结果343400