`a)-7/12 x+3/6=-8/4`
`→-7/12 x=-8/4-3/6`
`→-7/12 x=-5/2`
`→x=-5/2÷-7/12`
`→x=30/7`
Vậy `x=30/7`
`b)3/4|1/4 x-1/2|=1/6`
`→|1/4 x-1/2|=1/6:3/4`
`→|1/4 x-1/2|=2/9`
`→` \(\left[ \begin{array}{l}\dfrac{1}{4}x-\dfrac{1}{2}=\dfrac{2}{9}\\\dfrac{1}{4}x-\dfrac{1}{2}=\dfrac{-2}{9}\end{array} \right.\)
`→` \(\left[ \begin{array}{l}\dfrac{1}{4}x=\dfrac{13}{18}\\\dfrac{1}{4}x=\dfrac{5}{18}\end{array} \right.\)
`→` \(\left[ \begin{array}{l}x=\dfrac{26}{9}\\x=\dfrac{10}{9}\end{array} \right.\)
Vậy `x∈{26/9;10/9}`
`c)5x=3y→x/3=y/5` mà `x-y=10`
Áp dụng tính chất dãy tỉ số bằng nhau ta có:
`x/3=y/5=(x-y)/(3-5)=10/(-2)=-5`
`→x/3=-5→x=(-5).3=-15`
`→y/5=-5→y=(-5).5=-25`
Vậy `(x;y)=(-15;25)`
