`7) 2x(x-5) -7(5-x) =0`

`<=> 2x(x-5) +7(x-5) =0`

`<=> (x-5)(2x+7) =0`

`<=> [(x-5=0),(2x+7=0):}`

`<=> [(x=5),(x=-7/2):}`

Vậy `x in {5;-7/2}`

`8) 3x(x-2) +2(x-2) =0`

`<=> (x-2)(3x+2) =0`

`<=> [(x-2=0),(3x+2=0):}`

`<=> [(x=2),(x=-2/3):}`

Vậy `x in {2;-2/3}`

`9) x(3x+2) -x(2x+3) =0`

`<=> 3x^2+2x-2x^2-3x=0`

`<=> x^2-x=0`

`<=> x(x-1) =0`

`<=> [(x=0),(x-1=0):}`

`<=> [(x=0),(x=1):}`

Vậy `x in {0;1}`

`10) 5x(x-1) =x-1`

`<=> 5x(x-1) -(x-1) =0`

`<=> (x-1)(5x-1) =0`

`<=> [(x-1=0),(5x-1=0):}`

`<=> [(x=1),(x=1/5):}`

Vậy `x in {1;1/5}`

`11) x(x+2)-x-2=0`

`<=> x(x+2) -(x+2) =0`

`<=> (x+2)(x-1) =0`

`<=> [(x+2=0),(x-1=0):}`

`<=> [(x=-2),(x=1):}`

Vậy `x in {-2;1}`

`12) x(x-2) +x-2=0`

`<=> x(x-2) +(x-2) =0`

`<=> (x-2)(x+1) =0`

`<=> [(x-2=0),(x+1=0):}`

`<=> [(x=2),(x=-1):}`

Vậy `x in {2;-1}`

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