In the figure ABCD is a cyclic quadrilateral whose side AB is a diameter of the circle through A , B , C and D. If ∠ADC = 120°, find ∠BAC.

Dear student,ABCD is cyclic quad.So, sum of opposite angles are 180.D+B=180120+B=180B=60-----(1)AB is diameter. Diameter subtends 90 on circumference of circle.ACB=90----(2)In ABC,BAC+CBA+ACB=180 (sum of interior angles of )90+60+BAC=180BAC=30Regards

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