`=>`Gợi ý:
`7/12 - 2/7 + 1/12`
`= (7/12 + 1/12) - 2/7`
`= 2/3 - 2/7`
`= 8/21`
\(\dfrac{7}{12}-\dfrac{2}{7}+\dfrac{1}{12}\)
\(=\left(\dfrac{7}{12}+\dfrac{1}{12}\right)-\dfrac{2}{7}\)
\(=\dfrac{2}{3}-\dfrac{2}{7}\)
\(=\dfrac{14}{21}-\dfrac{6}{21}=\dfrac{14-6}{21}=\dfrac{8}{21}\)