# 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.

- 5
^{2}= x^{2}+ y^{2} - 1 = x
^{2}+ y^{2}– 4x – 4y

*Guide: *

The equation of a circle

(x-a)^{2} + (y-b)^{2} = r^{2}

Where

- Center = (a,b)
- Radius = r

General form of circle equation

ax^{2} + by^{2} + 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)**

- Radius = 5, Centre = (0,0)
- Radius = 3, Centre = (2,2)

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