Có: \(\frac{2}{a\left(a+1\right)\left(a+2\right)}=\frac{\left(a+2\right)-a}{a\left(a+1\right)\left(a+2\right)}=\frac{a+2}{a\left(a+1\right)\left(a+2\right)}-\frac{a}{a\left(a+1\right)\left(a+2\right)}\)\(=\frac{1}{a\left(a+1\right)}-\frac{1}{\left(a+1\right)\left(a+2\right)}\)
Có: \(\frac{2}{a\left(a+1\right)\left(a+2\right)}=\frac{2+\left(a-a\right)}{a\left(a+1\right)\left(a+2\right)}=\frac{2+a}{a\left(a+1\right)\left(a+2\right)}-\frac{a}{a\left(a+1\right)\left(a+2\right)}\):
Rút gọn các phân số, ta được: \(\frac{1}{a\left(a+1\right)}-\frac{1}{\left(a+1\right)\left(a+2\right)}\)
Bạn hiểu chưa?