+129850 Let (x,y) be the center
Since all radiuses are equal the distance from the center to any of the points is equal
So we can solve this using (-7,10) and (5,4)
(x + 7)^2 + ( y -10)^2 = (x - 5)^2 + ( y - 4)^2 simplify
x^2 + 14x + 49 + y^2 - 20y + 100 = x^2 -10x + 25 + y^2 -8y + 16
24x - 12y = -108 ⇒ 2x - y = - 9 ⇒ y= 2x + 9 (1)
And using (-7,10) and (15, -10)
(x + 7)^2 + (y-10)^2 = (x -15)^2 + ( y +10)^2
x^2 + 14x + 49 + y^2 - 20y + 100 = x^2 -30x + 225 + y^2 + 20y + 100
44x - 40y = 176
11x - 10y = 44 (2)
Sub (1) into (2)
11x - 10 ( 2x + 9) = 44
11x -20x - 90 = 44
-9x = 134
x= -134/9
y = 2(-134/9) + 9 = -187/9
