Tìm x a) 5(x-3)-2(x+6)=9 b) 5(x-7)+10(3-x)=20 c) -4(x+1)+8(x-3)=24 d) 7(5-x)+5(x-2)=15

Đáp án:

`a) x = 12`

`b) x = - 5`

`c) x = 3`

`d) x = 5`

Giải thích các bước giải:

`a) 5 . ( x - 3 ) - 2 . ( x + 6 ) = 9`

`=> 5x - 15 - 2x - 12 = 9`

`=> 5x - 2x = 9 + 15 + 12`

`=> 3x = 24 + 12`

`=> 3x = 36`

`=> x = 36/3 = 12`

Vậy `x = 12`

`b) 5 . ( x - 7 ) + 10 . ( 3 - x ) = 20`

`=> 5x - 35 + 30 - 10x = 20`

`=> ( 5x - 10 ) = 20 + 35 - 30`

`=> - 5x = 55 - 30`

`=> - 5x = 25`

`=> x = 25/(-5) = - 5`

Vậy `x = - 5`

`c) - 4 . ( x + 1 ) + 8 . ( x - 3 ) = 24`

`=> - 4x - 4 + 8x - 24 = 24`

`=> 8x - 4x = 24 + 24 + 4`

`=> 4x = 48 + 4`

`=> 4x = 52`

`=> x = 52/4 = 13`

Vậy `x = 3`

`d) 7 . ( 5 - x ) + 5 . ( x - 2 ) = 15`

`=> 35 - 7x + 5x - 10 = 15`

`=> 5x - 7x = 15 - 35 + 10`

`=> - 2x = - 20 + 10`

`=> - 2x = - 10`

`=> x = (-10)/(-2) = 5`

Vậy `x = 5`