2.f(x)>= a is a constant, so it only needs f min >; =a .

In other words, the problem of constant establishment can be transformed into the problem of finding the maximum value of a function.

Find the maximum value by discriminant

It is mainly suitable for functions that can be transformed into quadratic equations about independent variables.

Monotonicity of function

Firstly, the monotonicity of the function in a given interval is determined, and then the maximum value of the function is obtained according to the monotonicity.

Number-shape combination

It is mainly suitable for functions with clear geometric figures, and the maximum value of the function can be found through geometric models.