Centre and Radius of a circle

Centre and Radius of a circle (Question)

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

  1. 52 = x2 + y2
  2. 1 = x2 + y2 – 4x – 4y


The equation of a circle
(x-a)2 + (y-b)2 = r2

  • Center = (a,b)
  • Radius = r

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

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

Centre and Radius of a circle (Answer)

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

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