Using <span>Descartes' rule of signs. There are 4 changes of signs of coefficients: + to - (+x^6-x^5) - to + (-x^4+4x^3) + to - (+4x^3-12x^2) - to + (-12x^2+12) Therefore, there are 4,2 or 0 positive roots </span><span><span>at most</span>. So it must be the third answer. </span>