2. Make the derivative function equal to 0, and find the extreme point x= root number A..

3. So it decreases in the interval (0, root number A) and increases in [root number A,+infinity].

4. The second problem is to discuss the sizes of radical numbers A and 1 and 2, which are divided into three situations: less than or equal to1; Greater than 1 less than 2; Greater than or equal to 2.

5. Use the monotonicity of step 3 to discuss the maximum values of the above three situations and write the answers respectively.