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# Core/Pure 1 Homework on Circles watch

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1. I've got this homework and I am totally confused because the questions are nothing like we did in class. I've done over 2/3, but I'm completely lost on some of them.

Here's one:

- The y-axis is a tangent to the circle which crosses the x-axis at (8,0) and (18,0)

(i) Find the radius of this circle and co-ords of its centre.

(ii) Find the equation of the circle in form x2 + y2 + px + gy + r = 0
2. (Original post by and87)
I've got this homework and I am totally confused because the questions are nothing like we did in class. I've done over 2/3, but I'm completely lost on some of them.

Here's one:

- The y-axis is a tangent to the circle which crosses the x-axis at (8,0) and (18,0)

(i) Find the radius of this circle and co-ords of its centre.

(ii) Find the equation of the circle in form x2 + y2 + px + gy + r = 0
is there any point doing this seeing as the exam has been?
3. Every point seeing as my exam for C1 is in June.
4. (Original post by and87)
Every point seeing as my exam for C1 is in June.
Didnt you have any core 1/core 2 modules this time round?
5. No. I've got both core exams in May/June period. I had discrete yesterday.
6. This is quite a guess as i am quite pissed!

I think the radus will be 13, (the mid-point between 8 and 18 is 13, and as the y-axis is the tangent, 13 will also be the x-value for the mid point)

Im thinking about it but thats al i have, but ill try when sober!
7. (Original post by DOJO)
Didnt you have any core 1/core 2 modules this time round?
My school doesnt believe in Jan modules so I take c1-4, m1 + s1 in the Summer! Should be entertaining...
8. (Original post by and87)
Every point seeing as my exam for C1 is in June.
Oh, sorry i was completely oblivious to the fact that some people are having them in June. Sorry, i only wish mine would have been then!
9. (Original post by and87)
I've got this homework and I am totally confused because the questions are nothing like we did in class. I've done over 2/3, but I'm completely lost on some of them.

Here's one:

- The y-axis is a tangent to the circle which crosses the x-axis at (8,0) and (18,0)

(i) Find the radius of this circle and co-ords of its centre.

(ii) Find the equation of the circle in form x2 + y2 + px + gy + r = 0
Draw the circle, touching y axis and crossing x axis at given points.

draw x=13. This bisects AB where A is 8,0 and B is 18,0

You can now see the centre must lie on x=13, and so the radius is 13, since the distance between the point where the circle touches the y axis and x=13 is 13.

You have a couple of nice 5,12,13 triangles between A,B, and O. (the centre)
which allow you to locate the centre. Then build your equation.

Aitch
10. Isnt this circle stuff in C2?
11. (Original post by sash37uk)
Isnt this circle stuff in C2?
It was in P3 when I did it!

Aitch
12. (Original post by Aitch)
It was in P3 when I did it!

Aitch
Yeah, same. But they've put it in C2 now.

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Updated: January 14, 2005
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