Circle A has radius 5, and Circle B has radius 2. If CD = 12 and is a common
tangent, what is AB?

Answer:
[tex]3\sqrt{17}$ or \approx 12.37$ Units[/tex]
Step-by-step explanation:
In the attached diagram
CA=CO+OA
CO=DB
Therefore:
5=2+OA
OA=3 Units
The angle between a tangent line and a radius is 90 degrees. therefore triangle OAB is a right triangle with:
OB=12 units
OA=3 units
Using Pythagoras theorem
[tex]AB=\sqrt{3^2+12^2}\\ =\sqrt{153}\\=3\sqrt{17}$ or \approx 12.37$ Units[/tex]