x Turn on thread page Beta
 You are Here: Home >< Maths

# How to find the radius of a circle watch

1. The centre of a circle I have is 6,8 Can i find out the radius from ths info?
2. (Original post by SunDun111)
The centre of a circle I have is 6,8 Can i find out the radius from ths info?
Only if you know another point lying on the circumference of the circle.
3. Not just from the centre, so I'm guessing you probably have an equation looking like (x-6)^2+(y-8)^2?
Those equations are in the form (x-a)^2+(y-b)^2=radius^2
Hope that helps
4. (Original post by Zacken)
Only if you know another point lying on the circumference of the circle.
I have the coordinates of the tangent, its 9,12?
5. (Original post by SunDun111)
I have the coordinates of the tangent, its 9,12?

How do you find the length of the blue line (the radius), you know how to use the distance between two points formula, don't you?
6. (Original post by SunDun111)
I have the coordinates of the tangent, its 9,12?
It's the hypotenuse of the triangle from the centre of the circle to the point. r=sqrt((x-a)^2+(y-b)^2)
7. (Original post by Zacken)

How do you find the length of the blue line (the radius), you know how to use the distance between two points formula, don't you?
(Original post by XOR_)
It's the hypotenuse of the triangle from the centre of the circle to the point. r=sqrt(x^2+y^2)
Did it thanks
8. (Original post by SunDun111)
Did it thanks
Cheers.
9. (Original post by SunDun111)
Did it thanks
sorry, error: r=sqrt((x-a)^2+(y-b)^2)
10. (Original post by Zacken)
Cheers.
a question on trig identities,

If i had CosxSinx (multiplied together) all over Cos X, do the Cos's cancel so its just Sinx.
11. (Original post by SunDun111)
a question on trig identities,

If i had CosxSinx (multiplied together) all over Cos X, do the Cos's cancel so its just Sinx.
Yes.

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: May 1, 2016
Today on TSR

### How do I turn down a guy in a club?

What should I do?

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