O is the circumcentre of DeltaABC, given...

O is the circumcentre of `DeltaABC`, given `/_BAC = 85^@ and /_BCA = 55^@`, find `/_OAC`.

A

`40^(@)`

B

`50^(@)`

C

`60^(@)`

D

`80^(@)`

Verified by Experts

The correct Answer is:

B

`angle ABC = 180^@- (85^@+ 55^@) = 40^@`
`therefore angle COA = 40^@ xx 2 = 80^@`
`therefore angle OAC = (180-80)/2=50^@`

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