In the given figure,C and D are points on a semicircle described on AB as diameter. ∠ABD=75∘ and ∠DAC=35∘. What is ∠BDC?
∠ADB=90
In△ADB
∠DAB=180−90−75=15 (Angle on the Diameter)
∠CAB=∠CAD+∠DAB=35+15=50
ABCD is a cyclic quadrilateral which implies opposite angles are supplementary
∠CDB+∠CAB=180
∠CBD=180−50=130∘