Angle in a major segment is.
Given : A minor segment AB of a circle and two points C and D in BA and AB. respectively.
To prove : angle ACB is acute
Construction : Join OA and OB
We know that angle subtended by an arc of a circle at its center is twice the angle subtended by it at any point of the alternate segment of circle. Since AB is minor arc and angle ACB is the angle formed by it in alternate segment.
∴,2∠ACB=∠AOB.
=2∠ACB<180∘ ( since ∠AOB is an angle of triangle AOB)
=∠ACB<90∘
=∠ACB is an acute angle.