In figure, if ∠OAB=400, then ∠ACB equals
∵OA=OB (radius of circle)
∴∠OAB=∠OBA (angles opposite to equal sites)
∠OBA=400
In right angled ΔOAB
∠OAB+∠OBA+∠AOB=1800
400+400+∠AOB=1800
∠AOB=1800–800
∠AOB=1000
We know that
∠ACB=12∠AOB
=12×1000=500
Thus, (A) is correct.