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# 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

Guide:

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

• 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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