Question

Find the intervals in which the function given by $f\left(x\right)=4x^3-6x^2-72x+30$ is

i) Strictly increasing ii) Strictly decreasing

Answer 1

$f\left(x\right)=12x^2-12x-72=12[x^2-x-6]=12\left[\right(x+2\left)\right(x-3\left)\right]\text{strictly increasing in}(-\infty ,-2)(3,\infty )\text{decreasing in}(-2,3)$