Two identical circles touch at the point P(9,3)
one of the circles has equation x^2 + y^2 - 10x - 6y +18 = 0
find the equation of the other circle
x^2 + y^2 - 10x - 6y + 18 = 0 complete the square on x, y
x^2 - 10y + 25 + y^2 - 6y + 9 = -18 + 25 + 9 simplify
(x - 5)^2 + ( y - 3)^2 = 16
The center of this circle is ( 5 , 3) and the radius is 4
Then if the circles touch at (9,3) and they are identical....then this will be the midpoint of both centers
So.....let the center of the other circle be (h, k)..so we have
[ 5 + h) / 2 = 9 (3 + k) / 2 = 3
5 + h = 9*2 3 + k = 3*2
5 + h = 18 3 + k = 6
h =13 k = 3
The equation of the second circle is ( x -13)^2 + ( y - 3)^2 = 16
Here's a graph : https://www.desmos.com/calculator/efoxyb9720