在运用导数求单调性的问题中,我们常见到利用逆向思维来命制试题,即已知函数y=f(x)在区间(a,b)上的单调性,探求某个参数的范围.而函数y=f(x)求导后是二次函数或者经转化后是二次函数,这样的解题思路常有四种,下面举例说明. In the problem of using monotony to find monotonicity, we often use reverse thinking to order test questions, that is, the monotonicity of the known function y=f(x) in the interval (a,b), and the search for the range of a certain parameter. The function y=f(x) is a quadratic function after the derivation, or it is a quadratic function after the transformation. There are often four types of problem-solving ideas.