1) $(6x^5y^2-9x^4y^3+15x^3y^4):3x^3y^2
$=2x^2-3xy+5y^2$
2) $2x^4-5x^2+x^3-3-3x$
$=2x^4-6x^2+x^3-3x+x^2-3$
$=(x^2-3).(2x^2+x+1)$
Do đó : $(2x^4-5x^2+x^3-3-3x ):(x^2-3) = 2x^2+x+1$
3) $(x-y-z)^5 : (x-y-z)^3$
$=(x-y-z)^2$
4) $(x^2+2x+x^2-4):(x+2)$
$=[x.(x+2)+(x+2)(x-2)]:(x+2)$
$=(x+2).(2x-2):(x+2)$
$=2x-2$