1.1x(乘号)2+2x3+3x4+.+100x101=?
=1/3x100x101x102=343400
2.1x2+2x3+3x4+.+n(n+1)=?
=1/3xNx(N+1)x(N+2)
3.1x2x3+2x3x4+.+n(n=1)(n+2)=?
=1/4xNx(N+1)x(N+2)x(N+3)
1.1x(乘号)2+2x3+3x4+.+100x101=?
=1/3x100x101x102=343400
2.1x2+2x3+3x4+.+n(n+1)=?
=1/3xNx(N+1)x(N+2)
3.1x2x3+2x3x4+.+n(n=1)(n+2)=?
=1/4xNx(N+1)x(N+2)x(N+3)