Find the interval in which
`f(x)=x^(3)-3x^(2)-9x+20` is strictly increasing or strictly decreasing.

Find the interval in which f(x)=x^3-3x^2-9x+30 is strictly increasing or strictly decreasing.

f : (0, pi)to R, f(x)=2x+cot x . Find the intervals in which f(x) is strictly increasing or strictly decreasing.

Find the intervals in which f(x)=4x^(3)-45x^(2)+168x-16 is (i) Strictly increasing (ii) Strictly decreasing

Find the intervals in which f(x)=4x^(3)-45x^(2)+168x-16 is (i) Strictly increasing (ii) Strictly decreasing