You are Here: Home >< Maths

# circle geometry help watch

1. a circle passes through (0,2) and (0,8) and its centre lies on the line x=4.

what is the equation of the circle?

okay so I drew a sketch and appreciated that the centre of the circle must be (4,y)

but how do I find y? and how do I find the radius? thanks
a circle passes through (0,2) and (0,8) and its centre lies on the line x=4.

what is the equation of the circle?

okay so I drew a sketch and appreciated that the centre of the circle must be (4,y)

but how do I find y? and how do I find the radius? thanks
The distance from the centre of a circle to any point on its circumference is always the same - you can use this fact to find y.
3. (Original post by Mark13)
The distance from the centre of a circle to any point on its circumference is always the same - you can use this fact to find y.
so, y would be 4 too?
so, y would be 4 too?
No.

The distance from the centre to any point on the circle is always the same (the radius). Meaning:

Distance from (4,y) to (0,2) = Distance from (4,y) to (0,8)
5. (Original post by justinawe)
No.

The distance from the centre to any point on the circle is always the same (the radius). Meaning:

Distance from (4,y) to (0,2) = Distance from (4,y) to (0,8)
how do I find y from this?
how do I find y from this?
Don't you know the distance formula?
7. The equation of a circle is (x-h)^2 + (y-k)^2=r^2 where (h,k) are the coordinates of the centre of the circle, and x and y are the coordinates of any point on the circle, and r is the radius. Using the information you have, you will get two equations. Solve simultaneously to find k (the y coordinate of the centre of the circle) and then find r

*Yeah this is slightly more complicated, but it will work for any other question too :P

### Related university courses

TSR Support Team

We have a brilliant team of more than 60 Support Team members looking after discussions on The Student Room, helping to make it a fun, safe and useful place to hang out.

This forum is supported by:
Updated: March 27, 2013
Today on TSR

### Edexcel C3 Maths Unofficial Markscheme

Find out how you've done here

### 1,051

students online now

Exam discussions

Poll
Useful resources

### Maths Forum posting guidelines

Not sure where to post? Read the updated guidelines here

### How to use LaTex

Writing equations the easy way

### Study habits of A* students

Top tips from students who have already aced their exams