# Homework Help: Maths - Circle Theorems

1. Apr 24, 2005

### grahammm

Hi,

I am really confused with circle theorems, attached is a diagram and I need to find out ABC and CBO.

I have worked out that angle ACB is x degrees, and also know that angle OAC is equal to angle OBC.

But I don't know how to work out the what either are

Thanks

Graham

#### Attached Files:

• ###### maths.GIF
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2. Apr 24, 2005

### grahammm

Is this something to do with opposite angles on a cyclic quadratic add up to 180?

3. Apr 24, 2005

### whozum

If youcan post it on the web somewhere, we'd be able to see it before tomorrow. It has to be pre approved.

4. Apr 24, 2005

### grahammm

See www.kgmm.co.uk/maths.GIF[/URL]

Many thanks!

Graham

Last edited by a moderator: Apr 21, 2017
5. Apr 24, 2005

### whozum

Arc ABC? Angle ABC? You didnt label this angle.

Do you know anything specific about the inscription of the triangle in the circle? I want to say that the arcs between A B and C are 120 degrees, but I can't tell if thats whatits supposed to be.

6. Apr 24, 2005

### grahammm

Find in terms of X, expressions for the angles:

- ABC
- CBO

The points A,B, and C lie on the centre circle O.

7. Apr 24, 2005

### whozum

Since AC = BC, the triangle ABC is isosceles, and angles ABC and BAC are equal. The sum of all three angles is 180.
Where y is angle ABC
180 = 2y+x
y = 90-x/2