$\\$
`a,`
`3x-6y=3 (x-2y)`
$\\$
`b,`
`8x^3 - 2x=2x (4x^2 - 1)=2x [(2x)^2-1^2] =2x (2x-1)(2x+1)`
$\\$
`c,`
`-5m^3 (m+1) +m+1=-5m^3 (m+1)+(m+1)=(m+1)(-5m^3 + 1)`
$\\$
`d,`
`3(x-y)-5x (y-x)=3 (x-y) + 5x (x-y) =(x-y)(3+5x)`
$\\$
`đ,`
`3 (x^2-4)-(x+2)=3(x-2)(x+2)-(x+2)=(x+2) (3x - 6 - 1)=(x+2)(3x-7)`