Since AB is the diameter of the circle, ∴ \(\angle ACB\) is an angle in a semicircle = 90° ∴ \(\angle BCD = \angle ACD + \angle ACB = 40° + 90° = 130°\) ∴ \(\angle BAD = 180° - 130° = 50°\) [Because the opposite angles of a cyclic quadrilateral are supplementary]