Main Concept

If two internally tangent circles touch at $A$, and if $\mathrm{BD}$, $\mathrm{EF}$ are parallel diameters in the circles (such that $\mathrm{BD}$ points in the same direction as $\mathrm{EF}$), then $\mathrm{ADF}$ is a straight line. Alternately, if two externally tangent circles touch at $A$, and if $\mathrm{DB}$, $\mathrm{EF}$ are parallel diameters in the circles (such that $\mathrm{DB}$ points in the same direction as $\mathrm{EF}$), then $\mathrm{DAF}$ is a straight line.

$\mathrm{Radius} \left(\mathrm{CD}\right)$ =     

$\mathrm{Angle} \=$   

More MathApps

MathApps/AlgebraAndGeometry