Given that,

∠ACB is an angle in minor segment

To prove: ∠ACB > 90^o

Proof: By degree measure theorem

Reflex ∠AOB = 2 ∠ACB

And,

Reflex ∠AOB > 180^o

Then,

2 ∠ACB > 180^o

∠ACB >

∠ACB > 90^o

Hence, proved