问题描述:
数学计算题
最佳答案:
1x2+2x3+3x4+…+n(n+1)
=1^2+1+2^2+2+3^2+3+…+n^2+n
=(1^2+2^2+3^2+…+n^2)+(1+2+3+…+n)
=1/6*n(n+1)(2n+1)+1/2*n(n+1)
=1/6*n(n+1)(2n+1+3)
=1/6*n(n+1)(n+2)*2
=1/3*n(n+1)(n+2)
计算:1x2+2x3+3x4+...+n(n+1)
问题描述:
数学计算题
1x2+2x3+3x4+…+n(n+1)
=1^2+1+2^2+2+3^2+3+…+n^2+n
=(1^2+2^2+3^2+…+n^2)+(1+2+3+…+n)
=1/6*n(n+1)(2n+1)+1/2*n(n+1)
=1/6*n(n+1)(2n+1+3)
=1/6*n(n+1)(n+2)*2
=1/3*n(n+1)(n+2)