As we know, this quadratic function opens downward. In the words of junior high school students, on the left side of the symmetry axis, y increases with the increase of x; In the words of senior high school students, this function is monotonically increasing on the left side of the symmetry axis. Similarly, the function monotonically decreases on the right side of the symmetry axis. The left side of the symmetry axis is monotonically increasing and the right side is monotonically decreasing. Let's express it in intervals.

Because this function has an absolute value, pay attention to the classification discussion.