`***`Lời giải`***`
Câu 2.
a)
`(x-1)(4x-3)-4x(x-5)=5`
`<=>x(4x-3)-(4x-3)-4x(x-5)=5`
`<=>4x^2-3x-4x+3-4x^2+20x=5`
`<=>(4x^2-4x^2)+(20x-3x-4x)=5-3`
`<=>13x=2`
`<=>x=2/13`
Vậy `S={2/13}`
b)
`(x-1)^2-81=0`
`<=>(x-1)^2-9^2=0`
`<=>(x-1-9)(x-1+9)=0`
`<=>(x-10)(x+8)=0`
`+)x-10=0<=>x=10`
`+)x+8=0<=>x=-8`
Vậy `S={10;-8}`
Câu 3.
a)
`15x^2y-10xy^2`
`=5.3x^2y-5.2xy^2`
`=5xy(3x-2y)`
b)
`x^2-9+2xy+y^2`
`=(x^2+2xy+y^2)-9`
`=(x+y)^2-3^2`
`=(x+y+3)(x+y-3)`
