Plane Geometry Chapter 3: The Circle
Terms to Know:
Section 8: Tangents
- A tangent to a circle is a straight line which, however far it may be extended, has one and only one point in common with the circle. The one and only point is the point of contact or point of tangency.
- A polygon is circumscribed about a circle when its sides are tangent to the circle.
- The circle is the inscribed in the polygon.
Section 9: Equal Tangents
- By the length of a tangent from a point to a circle is meant the length of time from that point to the point of tangency.
- The line joining the points of tangency of two tangents drawn from an external point to a circle is called the chord of tangency of the two tangents.
Section 10-11: Common Tangents and Common Chords
- Two circles are tangent to each other if both are tangent to the same line at the same point.
- Two circles are tangent internally or externally, according to the tangent circles that lies wholly within or outside the other.
- A line that touches two circles is called a common internal tangent if both circles lie on opposite sides of the line.
- The length of a common tangent is the length of the line between the points of tangency.
- The line determined by the center of two circles is called the line of centers or the center line.
- The line segment joining the two centers is called the center segment.
- The common chord of two intersecting circles is the chord joining the points of intersection.