` 3x + 15 = 45 `
`3x = 45 - 15 `
`3x = 30`
`x = 30 : 3 `
`x = 10` vậy `x = 10`
` x - 4/7 = 8/5`
`x = 8/5 + 4/7 `
`x = 8 . 7 / 5 . 7 + 4 .5 / 7 . 5 `
`x = 56 / 35 + 20 / 35 `
`x = 56 + 20 / 35 `
`x = 76 / 35 `
vậy ` x = 76 / 35 `
`|x + 1/2 | = 3 / 4 `
TH1 : $x+\dfrac{1}{2}=\dfrac{3}{4}$
$x=\dfrac{3}{4}-\dfrac{1}{2}$
$x=\dfrac{1}{4}$
TH2:$x+\dfrac{1}{2}=\dfrac{3}{4}$
$x=-\dfrac{3}{4}-\dfrac{1}{2}$
$x=\dfrac{-5}{4}$
Vậy $x=\dfrac{1}{4}$ hoặc $x=\dfrac{-5}{4}$
