Let x 10 be f(x 1)>F(x2), which is a decreasing function; If f (x 1)-f (x2) < 0, that is, f (x 1) < F(x2) is increasing function.

2. In addition, there is a teaching method to judge in senior three. Let me give you a brief introduction. If the derivative of the function f(x) >; =0, then the function f(x) is increasing function;

If the derivative of the function f(x)

3. In fact, it can also be judged by image method. Intuitively, the greater the value of the independent variable of the function, the greater the value of the function, which depends on your own observation in the future.

However, as far as senior one is concerned, it is more about judgment.