Bài 44 : Tìm x biết:

`a) 2x - 3 = x + 1/2 `

`<=> 2x - x = 1/2 + 3 `

`<=> ( 2 - 1 ) . x = 1/2 + 6/2 `

`<=> x = ( 1 + 6 )/2 `

`<=> x = 7/2 `

Vậy ` x ∈ { 7/2 } `

`b) 11/15 - ( 7/9 + x ) . 3/8 = 61/90 + x/3 `

`<=> 11/15 - 7/24 - 3/8 x = 61/90 + ( 30x )/90 `

`<=> 53/120 - 3/8 x = ( 61 + 30x )/90 `

`<=> 53/120 - 45/120 x = ( 61 + 30x )/90 `

`<=> ( 53 - 45x )/120 = ( 61 + 30x )/90 `

`<=> ( 3 ( 53 - 45x ))/360 = ( 4 ( 61 + 30x ))/360 `

`<=> 159 - 135x = 244 + 120x `

`<=> - 135x - 120x = 244 - 159 `

`<=> - 255x = 85 `

`<=> x = - 1/3 `

Vậy ` x ∈ { - 1/3 } `