ABCD is a cyclic quadrilateral in a circle with centre O. If ∠ADC = 130°; find ∠ BAC.
Here ∠ACB = 90°
(Angle in a semicircle is right angle)
Also, ∠ABC = 180° -∠ADC = 180° - 130° = 50°
(pair of opposite angles in a cy clic quadrilateral are supplementary)
By angle sum property of right triangle ACB,
∠BAC = 90° - ∠ABC = 90° - 50° = 40°