∠OAC=∠OBC=90∘ (∵The tangent at any point on a circle is perpendicular to the radius throughthat point.)
∠OAC+∠OBC+∠ACB+∠AOB=360∘ (∵Sum of angles of a quadrilateral)
90∘+90∘+75∘+∠AOB=360∘
∠AOB=360∘−255∘=105∘ ∠AOB=105∘
In the figure given below, O is the center of the circle, CA istangent at A and CB is tangent at B drawn to the circle. If ∠ ACB=75∘, then ∠AOB= ______.