And if a common tangent of two circles makes the two circles on both sides of a straight line, this common tangent is called the inner common tangent.
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.
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.
Extended data:
A straight line connecting two centers of the circle is called a connecting line. When two circles are tangent, the tangent point is on the connecting line.
When two circles circumscribe each other, is the center distance o? o？ =R﹢r-r, (let the radius of the big circle be r and the radius of the small circle be r).
When two circles are inscribed, the center distance o? o？ =R﹣r？
The straight line connecting two circles or its extension line must pass through the tangent point.
1. In a triangle, the intersection of bisectors of three angles is the center of the inscribed circle, and the vertical segments from the center to each side of the triangle are equal.
2. A regular polygon must have an inscribed circle, and the center of the inscribed circle coincides with the center of the circumscribed circle, both of which are at the center of the regular polygon.
3. Common auxiliary lines: perpendicular to the center of the circle.
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