In the above figure O is the centre of the circle ∠AOB = 80∘ ,then complete the matching.
AngleValue1. ACB a. 90∘2. ADBb. 40∘3. ABCc. 80∘4. AOCd. 180∘
a-4, b-3, c-2, d-1
AOC is a straight line, so ∠AOC should be a straight angle. Therefore ∠AOC= 180∘
Diameter is also a chord of the circle .The angle subtended by AC at the centre is ∠AOC = 180∘
Since angle subtended by a chord at the center is equal to twice the angle subtended by chord at any point on the circle,
We get ∠AOC = 2 ∠ABC
∠ABC = 90∘
Similarly, ∠ADB = 12 ∠AOB
∠ACB= 12 ∠AOB
From the above equations we can see that ∠ADB = ∠ACB = 12 ∠AOB
∠ADB = ∠ACB = 40∘