1 circumscribed circle: The circle that intersects all vertices of a polygon is called the circumscribed circle of the polygon, which is usually used for convex polygons, such as triangles. If a circle just passes through three vertices, it is called the circumscribed circle of a triangle, and the circle just surrounds the triangle.

2. Inscribed circle: Mathematically, if each side of a polygon on a two-dimensional plane can be tangent to a circle inside it, then this circle is the inscribed circle of this polygon, and then this polygon is called a circle circumscribed polygon. It is also the largest circle in a polygon. The center of the inscribed circle is called the center of the polygon.

3, inscribed circle: usually for another circle, if a circle is in another big circle, the two circles have only one common point, this circle is called inscribed circle of the big circle.

4. circumscribed circle: circumscribed circle refers to another circle. If two circles have only one common point and the distance between the centers is equal to the sum of the radii of the two circles, the two circles are tangent to each other. When two circles are circumscribed, there are three common tangents.