Lời giải :
`a)(x-3)(x-1)-3(x-3)=(x-3)(x-3-3)=(x-3)(x-6)`
`b)(x-1)(2x+1)+3(x-1)(x+2)(2x+1)=(x-1)(2x+1)[1+3(x+2)]=(x-1)(2x+1)(1+3x+6)=(x-1)(2x+1)(3x+7)`
`c)(6x+3)-(2x-5)(2x+1)=3(2x+1)-(2x-5)(2x+1)=(2x+1)(3-2x+5)=(2x+1)(8-2x)=(2x+1).2.(4-x)`
`d)(x-5)^2+(x+5)(x-5)-(5-x)(2x+1)=(x-5)^2+(x+5)(x-5)+(x-5)(2x+1)=(x-5)(x-5+x+5+2x+1)=(x-5)(4x+1)`
`e)(3x-2)(4x-3)-(2-3x)(x-1)-2(3x-2)(x+1)=(3x-2)(4x-3)+(3x-2)(x-1)-(3x-2)(2x+2)=(3x-2)(4x-3+x-1-2x-2)=(3x-2)(3x-6)=3(3x-2)(x-2)`