Đáp án:
Giải thích các bước giải:
$ \text{abc=2}\\
\dfrac{a}{ab+a+2}+\dfrac{b}{bc+b+1}+\dfrac{2c}{ac+2c+2}\\
=\dfrac{a}{ab+a+2}+\dfrac{ab}{abc+ab+a}+\dfrac{2}{a+2+\frac{2}{c}}\\
=\dfrac{a}{ab+a+2}+\dfrac{ab}{2+ab+a}+\dfrac{2}{a+2+ab}\\\quad\text{do abc=2}\\
=\dfrac{a+ab+2}{a+ab+2}=1$