Angle in a minor segment is.
Given: A minor segment AB of a circle and two points C and D in BA and AB. respectively.
To prove: angle ADB is obtuse.
Construction: Join OA and OB
BA is the major arc and angle ADB is the angle formed by it in the alternate segment
∴2∠ADB=m(arcBA)
=2∠ADB=360∘−m(arcAB)
=2∠ADB=360∘−∠AOB(since(arcAB)=angleAOB)
=2∠ADB>360∘−180∘(∵∠AOB<180∘)
=∠ADB>90∘
=∠ADB is obtuse.