# How do we find these angles? Someone please explain.

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#1
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3 years ago
#2
(Original post by thebrahmabull)
For question R : consider the cyclic quadrilaterial PQRS.
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3 years ago
#3
Is it bad that I got an A in Maths and FM and don't know...

Circle Theorems have never been my friend.
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3 years ago
#4
(Original post by FailedMyMocks)
Is it bad that I got an A in Maths and FM and don't know...

Circle Theorems have never been my friend.
1
3 years ago
#5
In R, Using the cyclic quadrilaterial rule in circle theorem you should see that Q + O = 180 degrees so 180 -115 = 65 degrees. Using that, you can work out the angle of ROS.
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3 years ago
#6
(Original post by cameronleid_)
In R, Using the cyclic quadrilaterial rule in circle theorem you should see that Q + O = 180 degrees so 180 -115 = 65 degrees. Using that, you can work out the angle of ROS.
OPQR is not a cyclic quadrilateral so this is incorrect.

It should be clear that angle POR is not 65 degrees.
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3 years ago
#7
Is it 115, cos angle at centre is double circumference
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3 years ago
#8
(Original post by timif2)
Is it 115, cos angle at centre is double circumference
No that's not right. There is no chord that subtends both angles so you can't use that circle theorem for those angles.
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3 years ago
#9
An alternative to the method I gave above is to see that the major arc PSR subtends the reflex angle POR at the centre and PQR at the circumference so you can use the "angle at the centre" circle theorem and go from there.

But I think this method is confusing for most students.
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3 years ago
#10
ignore me
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3 years ago
#11
Deleted comment.
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3 years ago
#12
(Original post by SumOfSquares)
x
Hi, a hint for this method was already given above. Please read the posting guidelines, particularly the point about posting bigger hints. Thanks
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3 years ago
#13
(Original post by Notnek)
Hi, a hint for this method was already given above. Please read the posting guidelines, particularly the point about posting bigger hints. Thanks
Sorry. Should I delete the post?
1
3 years ago
#14
(Original post by SumOfSquares)
Sorry. Should I delete the post?
That would be great if you could. Please continue to help in the maths forum but always check the previous posts.
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