Coordinate geometry question

Hi, doing some questions on mymaths but i get a surd and it doesnt allow me to put a sqr root so im thinking i've gone wrong somewhere:

Find the equation of a circle which passes through A. B and C.

A (9,8) B (9,4) C (3,4)

ok so i first worked out the midpoint of AC to get the centre.

9+3/2=6
8+4/2=6

so the centre is (6,6)

So now i have (x-6)^2 + (y-6)^2

Now to work out the radius i did pythag of:

(9-3)^2+(8-4)^2=AC^2=52

So the radius is 1/2 x root52 no?

(edited 9 years ago)

Reply 1

gdunne42

in the the circle equation it = r^2 not r
so no root sign is required in the answer
Be very careful when you evaluate half of root 52. Personally I'd work out the radius by pythag from the centre of the circle.to A