In the given figure, O is the centre of the circle and ∠BDC = 42°. The measure of ∠ACB is
Construction: Join A and D.
Since AC is the diameter. So ∠ADC will be 90°.
`angleADB = 90 - angleBDC`
= 90 - 42
`angle ADB = 48°`
∠ACB = ∠ADB = 48° (Angle in the same segment are equal.)