# Common Tangents

Pronunciation: /ˈkɒm.ən ˈtæn.dʒəntz/ Explain

 Click on the blue points and drag them to change the figure. What can you say about the circles if they have only two common tangents? What can you say about the circles if they have four common tangents? Manipulative 1 - Common Tangents of Two Circles Created with GeoGebra.

Each pair of circles in a plane have zero, two or four tangent lines in common. If one of the circles is completely contained within the other, they have no common tangents. If the circles intersect, they have two tangent lines in common. If the circles do not intersect and one is not contained by the other, they have four tangent lines in common. These tangent lines are called the common tangents of the circles.

### References

1. McAdams, David E.. All Math Words Dictionary, common tangent. 2nd Classroom edition 20150108-4799968. pg 37. Life is a Story Problem LLC. January 8, 2015. Buy the book
2. common tangent. McGraw-Hill Dictionary of Scientific and Technical Terms. McGraw-Hill Companies, Inc.. 1974. Last Accessed 6/25/2018. http://www.answers.com/topic/common-tangent.
3. Shlomo Libeskind. Euclidean and Transformational Geometry: A Deductive Inquiry. pp 110-112. Jones & Bartlett Publishers. November 1 2007. Last Accessed 6/25/2018. Buy the book
4. Ray C. Jurgensen, Richard G. Brown, and John W. Jurgensen. Geometry. pg 334. Houghton Mifflin McDougal Littell. January 2000. Last Accessed 6/25/2018. Buy the book

McAdams, David E. Common Tangents. 12/21/2018. All Math Words Encyclopedia. Life is a Story Problem LLC. https://www.allmathwords.org/en/c/commontangents.html.

### Revision History

12/21/2018: Reviewed and corrected IPA pronunication. (McAdams, David E.)