How to define an increasing or decreasing function?

In order to determine whether the function is increasing or decreasing, you need to carry out several actions to study the function. First, we recall that an increasing function is considered to be such a function whose value Y will increase with an increase in the value of X and vice versa, a function in which Y will decrease with an increase in X will be considered to be decreasing. find the extremum points of the function. For a linear function, the derivative is equal to a constant (number) and is monotonic over the entire length. Determine the sign of the derivative before and after the extreme point. If the derivative is negative, then the function decreases in the specified interval, and if the derivative is positive, the function increases in this interval.