Answer:
Thales theorem is a corollary of the theorem, which states that the angle subtended by an arc at any point on the circumference is half of the angle subtended by it at the centre. For example if the arc AC
subtends angle ∠AOC
at the centre and ∠ABC
any where else on the circumference,
∠ABC=12∠AOC
and if AOC
is a diameter, it forms an angle of 180∘
and angle subtended by it at any point on circumference is
12×180∘=90∘