6.
7.
8.
- solvefor to obtaindoubleroot.
The slopeof the line from to , whichis the negativereciprocalof the slopeof the
line.
This meansthat the tangentline and radiusare perpendicular.CommonTangentsand TangentCircles
LearningObjectives
- Solveproblemsinvolvingcommoninternaltangentsof circles.
- Solveproblemsinvolvingcommonexternaltangentsof circles.
- Solveproblemsinvolvingexternallytangentcircles.
- Solveproblemsinvolvinginternallytangentcircles.
Commontangentsto two circlesmay be internalor external.Acommoninternaltangentintersectsthe
line segmentconnectingthe centersof the two circleswhereasacommonexternaltangentdoesnot.
CommonExternalTangents
Hereis an examplein whichyou mightencounterthe use of commonexternaltangents.
Example 1
Find the distancebetweenthe centersof the circlesin the figure.