Thinking: x= 1 is the extreme point of f(x), so when x= 1, the reciprocal of f(x) is 0.

A= 1, find the monotone decreasing interval of f(x), that is, find the value range of x when the reciprocal of f(x) is negative.

I won't ask the remaining two questions for the time being. Now I teach junior high school, and I haven't seen it for several years.