Question

In figure, O is the centre of the circle. If angle OAC = 20° and angle OBC = 40° find angle AOB

Answer 1

I think the answer is following
Draw a chord AB
then line segment AO and line segment BO are bisectors of triangle CAB
it means that angle OAB is 20 degrees and OBA is 40 degrees
with triangle sum property
20+40+x=180
60+x=180
x=180-60
x=120 degrees
therefore angle AOB is 120 degrees

Answer 2

Answer:

I think the answer is following

Draw a chord AB

then line segment AO and line segment BO are bisectors of triangle CAB

it means that angle OAB is 20 degrees and OBA is 40 degrees

with triangle sum property

20+40+x=180

60+x=180

x=180-60

x=120 degrees

therefore angle AOB is 120 degrees