If a straight line intersects a curve at two points, and the two points are infinitely close and tend to overlap, then the straight line is the tangent of the curve at that point. In junior high school mathematics, if a straight line is perpendicular to the radius of a circle and passes through the outer end of the radius of the circle, it is said that the straight line is tangent to the circle.
Here, when "Other Geometry" is a circle or a straight line, there is only one intersection point (common point) between them, and when "Other Geometry" is a polygon, there is only one intersection point between the circle and each side of the polygon. This intersection is the tangent point.
In the picture below, the orange lines are tangent and the sky blue lines intersect.
Extended data:
A circle is tangent to a straight line:
The positional relationship between a circle and a straight line with only one intersection point (common point) is called the tangent of the circle and the straight line, and the common point is called the tangent point. In the figure, the straight line AB is tangent and the common point C is tangent.
The tangent of a circle has the following relationship with the radius of the tangent point, which is also an important theorem for us to discuss the tangent of a circle and a straight line. '
Theorem 1, the tangent of a circle is perpendicular to the radius of the tangent point.
Theorem 2: If two tangents of a circle are made from a point outside the circle, the length of the line segment between the point and the two tangents is equal, and the bisector of the included angle must pass through the center of the circle.