Question

choose the correct option
with complete explanation

Answer 1

since ABCD is a cyclic quadrilateral, sum of opposite angles will be 180. Thus angle A is 60 degree. also angle ADB is angle in semicircle, so angle ADB = 90 degree. by angle sum property angle DAB is 30 degree. cheers!

Answer 2

ABCD is a cyclic quadrilateral so sum of opposite angles will be 180°.
So, DAB+DCB=180°
       DAB=180-DCB ⇒180-120=60°
As,AB is diameter of circle we can say that ADB is angle of semicircle =90°
In triangle ADB sum of angles is 180°.
DAB+ADB+DBA=180°
60°+DBA+90°=180°
DBA=180-150
DBA=30°