Question -
Answer -
It is given that, AB and CD are diameter with center O and
We have to find 
Construction: Join the point A and D to form line AD
Clearly arc AD subtends 
at B and 
at the centre. Therefore, ∠AOD=2∠ABD=100°∠AOD=2∠ABD=100° …… (1)
Since CD is a straight line then
∠DOA+∠AOC=180° (Linear pair)∠DOA+∠AOC=180° Linear pair
Hence 