A circle is centered on point B. Points A, C and D lie on it's circumference.
If ABC measures 40 degrees, what does ADC measure?

The measure of the angle ADC is 20°

Explanation:

Given:

∠ABC = 40°

∠ADC = ?

We know:

Angle subtended at the center is twice the angle subtended at the circumference.

Thus,

∠ABC = 2 x ∠ADC

On substituting the value we get:

40° = 2 X ∠ADC

∠ADC = 20°

Therefore, the measure of the angle ADC is 20°

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