| PA-PB | min = 0; (It can be perpendicular to AB, and the focus of L is PA-PB=0)
The key is to find the maximum value of |PA-PB|;
Let pm = x, (0
PA-PB= under radical sign (16+x2)- under radical sign [1+(4-x) 2];
With the ability of junior high school, this formula is really difficult to answer. . . I don't know how to continue,
The first feeling is to ask for guidance directly, but I certainly haven't learned it in junior high school. This is a tragedy.
Let me think about it first. .
As shown in the picture, you have to learn to draw:
In this way, the problem is solved perfectly. . . All you have to do is draw pictures and explain them clearly.