This is a quadratic function. According to the image, as long as its symmetry axis is not in this interval, the image in this interval can only be single increase (only increase) or single decrease (only decrease). This is called monotonicity. (If the symmetry axis is in the interval, the function image will change from falling to rising. )

Calculate the symmetry axes less than 1 and greater than 4 respectively.

Don't tell me you don't know the symmetry axis formula!