Given: and

In ΔOAB

Here,

OA = OB (radius)

Let ∠OBA = ∠OAB = x (angles opposite to equal sides are equal)

By angle sum property

∠AOB + ∠OBA + ∠OAB = 180°

50° + x + x = 180°

2x = 180° – 50°

2x = 130°

x = 60°

∴ ∠OAB = 60°