(1) In (1), there is an interval for you (1, +∞), and then the interval given in (2) is to change the above 1 to-1, and then (/kloc-0) .

② First of all, it should be understood that this -lna is the maximum value of f(x) in the discussed interval. You can tell when you draw an image. It tells you that the maximum value is equal to zero, that is to say, there is only one intersection point between f(x) and X axis, that is, there is only one zero point. This step refers to the case that the maximum value is greater than zero, that is, there are two f(x) and X axis.

(3) For the interval mentioned here, from the negative first power of A to the power of a- 1 of E, the value of f(x) on the left is above the X axis, and the value on the right is below the X axis. Does that mean that if f(x) does not break in this interval, it must intersect with the X axis? In other words, the sentence you marked means that the function intersects the x axis, that is, there is. . .

④f(x) is a monotonically decreasing function in the discussed interval, that is to say, it can only go down from the point on the left of the interval, and it intersects with the X axis. Does it only go down after that intersection? . . . If you keep going down, you can't come up and cross the X axis. . . .

To discuss the zero point of a function is to look at the intersection of the function and the X-axis. It will be much easier to understand if you learn to express the image on grass paper. Finally, I give you a suggestion, that is, draw pictures often and express functional images as sketches as much as possible, which will be very helpful for your understanding.

In addition, I wish you progress and smooth study.