Need help with Circle Theorem Q's (Higher GCSE Level)

Hello everyone, I would appreciate some help with these Q's. I am currently in Year 11 taking GCSE Maths, and I am confused about these theorems (specifically on these Q's). Despite getting the second picture right, I am still hella unsure how I got it. Help?

Original post by TheKevinFang

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There's quite a lot here so can you post all your working/ideas and the specific parts you can't do.

Let us know if you have no idea for any of them then we can start at the beginning.

(edited 9 years ago)

Reply 2

TheKevinFang

OP

9

Original post by notnek

There's quite a lot here so can you post all your working/ideas and the specific parts you can't do.

Let us know if you have no idea for any of them then we can start at the beginning.

OK.

The second picture - all of it; just puzzled in general.

The first picture - The 3rd angle, I can find OAC, but to complete OAD, I cannot find CAD. I know it's something 25 degrees but why? I found this because it was the second attempt.

Hopefully you can help me easier now.

Regards,

Kevin.

Reply 3

Notnek

21

Original post by TheKevinFang

OK.

The second picture - all of it; just puzzled in general.

The first picture - The 3rd angle, I can find OAC, but to complete OAD, I cannot find CAD. I know it's something 25 degrees but why? I found this because it was the second attempt.

Hopefully you can help me easier now.

Regards,

Kevin.

Try considering the whole quadrilateral AOCD instead.

You're given one of the angles and 2 more can be found using circle theorems.

Reply 4

TheKevinFang

OP

9

Is the fact that line OC is perpendicular to line RT a theorem exactly? I know that in the quad AOCD, it's 134 + 92 (angle ABC x 2) + 65 (perpendicular so 90 - 25) which is then 291 degrees. So 360 - 291 = 69. Unsure still whether the 90 - 25 is still a circle theorem.
Thanks for dropping the hint though. Could you clear up the second larger picture for me please? I still am stuck on that one.

Reply 5

TenOfThem

18

Original post by TheKevinFang

Is the fact that line OC is perpendicular to line RT a theorem exactly? I know that in the quad AOCD, it's 134 + 92 (angle ABC x 2) + 65 (perpendicular so 90 - 25) which is then 291 degrees. So 360 - 291 = 69. Unsure still whether the 90 - 25 is still a circle theorem.
Thanks for dropping the hint though. Could you clear up the second larger picture for me please? I still am stuck on that one.