Angle AOB=80 ( angle subtended by an arc at centre of circle is double the angle subtended at any other point on the circle )
Therefore, angle OAB=angle OBA=x
2x +80=180 ( angle sum property of Triangle)
Hence, x= 50.

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Rimjim Das answered this

In the figure is zero In the given figure if O is the centre of the circle then find the x