ABCD is a cyclic quadrilateral such that AB is a diameter of the circle circumscribing it and ADC = 140º, then BAC is equal to:
(A) 80º
(B) 50º
(C) 40º
(D) 30º
(B) 50°
Solution:
Given, ABCD is cyclic Quadrilateral and ADC = 140°
We know that the sum the opposite angles in a cyclic quadrilateral is 180°.
ADC + ABC = 180°
140° + ABC = 180°
ABC = 180° – 140°
ABC = 40°
Since, ACB is an angle in semi circle
ACB = 90°
In ABC
BAC + ACB + ABC = 180° (angle sum property of a triangle)
BAC + 90° + 40° = 180°
BAC = 180° – 130° = 50°
Therefore option (B) is correct.