Question

MAB = 120 and AC is the diameter of this circle. What is the degree measure of BDC

Answer 1

mAB is 120, so m∠ADB is half of mAB=60
AC is the diameter, which means arc ABC is 180, and m∠ADC=90
m∠BDC=m∠ADC-m∠ADB=90-60=30
so the angle BDC is 30 degree