`y²-5y+2(y-5)=0`

`y²-5y+2y-10=0`

`y²-3y-10=0`

`y²-5y+2y-10=0`

`(y²+2y)-(5y+10)=0`

`y(y+2)-5(y+2)=0`

`(y-5)(y+2)=0`

`Th1:`

`y-5=0`

`y=5`

`Th2:`

`y+2=0`

`y=-2`

Vậy `y∈{5;-2}`

____________________

`9x²-1=(3x-1)(2x+7)`

`(3x-1)(3x+1)-(3x-1)(2x+7)=0`

`(3x-1)(3x+1-2x-7)=0`

`(3x-1)(x-6)=0`

`Th1:`

`3x-1=0`

`3x=1`

`x=1/3`

`Th2:`

`x-6=0`

`x=6`

Vậy `x∈{1/3;6}`