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# A quick C2 Q. watch

1. How do you find the equation again?

Coordinates:
A(5,-1)
B(13,11)

a.) Find the co-ords of the midpoint AB. ---> (9,5)

b.) AB is a diameter of the circle C, find an equation for C.
2. Ah , I just did that paper!
well since you know AB is the diameter, the centre of the circle is the midpoint of AB (9,5) . You can then put this into the equation so (x-9)^2 + (y-5)^2 = radius^2
Find radius by finding distance between midpoint and either a or b - take your pick!
franks x
3. (Original post by franks)
Ah , I just did that paper!
well since you know AB is the diameter, the centre of the circle is the midpoint of AB (9,5) . You can then put this into the equation so (x-9)^2 + (y-5)^2 = radius^2
Find radius by finding distance between midpoint and either a or b - take your pick!
franks x
(x-9)² + (y-5)² = [(√208)/2]²

Is that right?
4. Slice did you get My message?

Newton.
5. (Original post by Newton)
Slice did you get My message?

Newton.
Yup. I've just replied.
6. Um radius^2 = 4^2 + 6^2 = 52 I think !
7. (Original post by franks)
Um radius^2 = 4^2 + 6^2 = 52 I think !
Oh! I used the wrong co-ordinates. Used A&B again. Oops, my mistake.

Many thanks.
8. its ok

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