Bài 1: Chứng minh rằng \(\frac{1}{1.2.3}\)+ \(\frac{1}{2.3.4}\)+ ...+ \(\frac{1}{n\left(n+1\right)\left(n+2\right)}\)= \(\frac{n\left(n+3\right)}{4\left(n+1\right)\left(n+2\right)}\)
Bài 2: Chứng minh rằng 1.2.3 + 2.3.4 +...+ n(n+1)(n+2)= \(\frac{n\left(n+1\right)\left(n+2\right)\left(n+3\right)}{4}\)