1. Analytical Geometry
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2. Circle
 A circle is the set of all points in a plane that are equidistant
from a fixed point in the plane.
 The fixed point is called the centre of the circle .
 The distance from the centre to a point on the circle is
called the radius of the circle
Centre
o
A
C
B
Radius
OA = OB =OC
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3. Equation Of The Circle
 The equation of the circle is simplest if the centre of the
circle is at the origin.
 But the equation of the circle with a given centre and
radius
Given C (h, k) be the centre and r
the radius of circle.
Let P(x, y) be any point on the circle
Then,
by the definition,
| CP | = r .
By the distance formula,
X
Y
P (x , y)
C (h, k)
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4. We have
i.e.,
This is the required equation of the circle with centre at
(h, k) and radius r
rkyhx
22
222
rkyhx
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5. Examples
Find the equation of the circle with centre (–3, 2) and radius 4.
Solution:
Here h= –3, k= 2 and r= 4.
Therefore,
the equation of the required circle is
1623
22
yx
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6. The End
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