A circle is centered on point B. Points A, C and D lie on its circumference.
If ∠ADC measures 23 degree, what does ∠ABC measure?
An inscribed angle is half the measure of its intercepted arc, so
m∠ADC = (1/2)(m∠ABC)
Substitute 23° in for m∠ADC
23° = (1/2)(m∠ABC)
Multiply both sides by 2
46° = m∠ABC