`5/12-(-3/8-x)=-5/6`
`<=>5/12+3/8+x=-5/6`
`<=>x=-5/6-5/12-3/8`
`<=>x=-13/8`
Vậy `x=-13/8`
\(\dfrac{5}{12}-\left(-\dfrac{3}{8}-x\right)=-\dfrac{5}{6}\\ \dfrac{5}{12}+\dfrac{3}{8}+x=-\dfrac{5}{6}\\ x=-\dfrac{5}{6}-\dfrac{5}{12}-\dfrac{3}{8}\\ x=\dfrac{-20}{24}+\dfrac{-10}{24}+\dfrac{-9}{24}\\ x=\dfrac{-20-10-9}{24}\\ x=\dfrac{-39}{24}\\ x=-\dfrac{13}{8}\)