You must first determine the domain of the function.
2. The monotonicity of a function is for an interval, but for a single point, there is no monotonicity because its function value is the only definite constant.
Increase or decrease changes, so there is no monotonicity problem; In addition, the middle school mainly studies continuous functions or piecewise continuous functions. For closed intervals,
For a continuous function on, as long as it is monotonous in the open interval, it is monotonous in the closed interval. Therefore, when considering its monotonous interval, it includes
Do not include endpoints; Also note that for functions that are discontinuous at some points, the monotone interval does not include discontinuous points.