First of all, this function is an even function, and it is a increasing function on [0, ∏/2], so we can draw the "changing trend" image of this function. Then "look at the picture and talk", I believe you have solved it.

Functional problems, when not, what to consider? Just look at the nature of the function. This is the way to solve the function problem. In addition, draw at any time.

You should take the college entrance examination at once. Time is of course precious, so don't waste too much time. Wish you success!