A geometry problem by A Former Brilliant Member

Geometry Level 2

AB and CB are tangents to the circle. Find A D C \angle ADC in degrees.


The answer is 65.

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1 solution

The tangents to a circle drawn from an external point are equal, and make equal angles with the line joining the point to the center. A tangent line makes an angle of 90 degrees with the radius of the circle.

inscribed angle = 1 2 \frac{1}{2} i n t e r c e p t e d intercepted a r c arc

< A D C <ADC = = 1 2 \frac{1}{2} ( 65 (65 )( 2 2 ) = = 6 5 \boxed{65^\circ}

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