Is x+2 a factor of 3x^4+7x^3+3x^2-x-4?
lets check by putting x= - 23x^4+7x^3+3x^2-x-4=03(-2)^4+7(-2)^3+3(-2)^2+2-4=03*16-56+12-2=048-56+10=2=0 Nox+2 is not a factor