Centre and Radius of a circle


From the of the circles equations, determine the radius and also the centre.

  1. 32 = x2 + y2
  2. -30 = x2 + y2 – 6x – 10y


  1. Radius = 3, Centre = (0,0)
  2. Radius = 2, Centre = (3,5)

The equation of a circle
(x-h)2 + (y-b)2 = r2
Center = (h,b)
Radius = r

General form of circle equation
ax2 + by2 + cx + dy + e = 0

From General form of circle equation to The equation of a circle:
Perform completing the square on the two variables in the equation.

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