Find the interval in which f (x) = 2x³ + 3x² – 12x + 1 is increasing.

Find the interval in which f (x) = x³ – 3x² – 9x + 20 is strictly increasing or strictly decreasing.

Find the interval of increase or decrease of the 

The function f (x) = sin⁴ x + cos⁴ x increasing if:

 Then f decreases in the interval   

Find the interval for which f (x) = x – sin x is increasing or decreasing.

Where a is positive constant. Find the interval in which f’ (x) is increasing.

If a < 0, and f (x) = e^ax + e^–ax is monotonically decreasing. Find the interval to which x belongs.   

If f (x) = ax³ + bx² + cx + d where a, b, c, d are real numbers and 3b² < c², is an increasing cubic function and g(x) = af’ (x) + bf’’ (x) + c², then