`1)` `(x-5)(x-1)=(x-1)(x-2)`
`⇔(x-5)(x-1)-(x-1)(x-2)=0`
`⇔(x-1)(x-5-x+2)=0`
`⇔-3(x-1)=0`
`⇔x-1=0`
`⇔x=1`
`2)` `6(x-3)(x-4)-6x(x-2)=4`
`⇔6(x^2-4x-3x+12)-6x^2+12x-4=0`
`⇔6x^2-24x-18x+72-6x^2+12x-4=0`
`⇔-30x=-68`
`⇔x=34/15`
`3)` `-(x+3)(x-4)+(x-1)(x+1)=10`
`⇔-(x^2-4x+3x-12)+x^2-1=10`
`⇔-x^2+4x-3x+12+x^2-1=10`
`⇔x+11=0`
`⇔x=-11`