∵1×2+2×3+3×4=
1
3 ×3×4×5=20,即1×2+2×3+3×4=
1
3 ×3×(3+1)×(3+2)=20
∴(1)原式=
1
3 ×100×(100+1)×(100+2)=
1
3 ×100×101×102;
(2)原式=
1
3 n(n+1)(n+2);
(3)原式=
1
4 n(n+1)(n+2)(n+3).
∵1×2+2×3+3×4=
1
3 ×3×4×5=20,即1×2+2×3+3×4=
1
3 ×3×(3+1)×(3+2)=20
∴(1)原式=
1
3 ×100×(100+1)×(100+2)=
1
3 ×100×101×102;
(2)原式=
1
3 n(n+1)(n+2);
(3)原式=
1
4 n(n+1)(n+2)(n+3).