Question

观察下列等式1×2=1/3×1×2×3; 1×2+2×3=1/3×2×3×4;1×2+2×3+3×4=1/3×3

Answer 1

1×2+2×3+3×4=1/3×3×4×5

.

1×2+2×3+3×4+...+n×(n+1)=1/3×n×(n+1)×(n+2)

没见题目要求,我把规律替你找出来,自己去思考吧