math
posted by kathy on .
so i am in precalculus, we need to graph the fuction using derivatives, maxima, intercepts and concavity. I am having trouble factoring cubics: for example: x^44x^3+16x > x(x^34x^2+16)Now what? That is without calculator, how do you find the roots?

The equation x^34x^2+16=0 has 1 real root
x=1.68 (approx)
(x^44x^3+16x)'=4x^312x^2+16=4(x^33x^2+4)=4(x+1)(x^24x+4)=4(x+1)(x2)^2
(x^44x^3+16x)''=12x^224x=12x(x2)