① Separation: it means that the distance between centers is greater than the sum of radii;

(2) circumscribed: the center distance is equal to the sum of radii;

③ Intersection: center distance is greater than radius difference is less than radius sum;

④ Internal cutting: the center distance is equal to the radius difference;

⑤ Inclusion: the center distance is less than the radius difference.

2, the position relationship between straight line and circle:

① Separation: the distance from the center of the circle to the straight line is greater than the radius;

② Tangency: the distance from the center of the circle to the straight line is equal to the radius;

③ Intersection point: the distance from the center of a circle to a straight line and the radius of salted fish.

3. The relationship between straight line and straight line:

① Parallel: the slopes are equal (if any);

② Vertical: the slopes are mutually negative reciprocal (if there are slopes);

③ Intersection: nonparallel (coincidence is generally not considered in analytic geometry).