If the equation of circle is

Then center = (–g, –f)

and radius

Or

If the equation of circle is

By completing square,

** Example1: **Find the centre and radius of the circle

** Solution: **Comparing the given equation with the standard equation,

and c = 9

Centre

Radius

Therefore the circle has its centre and radius 4 units.

** Question 1:** Find the center and radius of the circle

** Solution 1: **This is of the form

Therefore the centre of the circle =

Comparing the two equations radius = 7 units

** Question 2: **Find the centre and radius of the circle

** Solution 2: **This is of the form

Comparing these two equations we get

and and can be rewritten as

Radius, units.

center =

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