C O N I C S E C T I O N S

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C O N I CS E C T I O N S
Part 2 The Circle
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(x-h)2(y-k)2r2
x y
Points on the circle.
Ellipse
Ellipse
h k
The center of the circle.
r
The radius of the circle.
Circle
Example (x1)2 (y3)2 20
Center location
( -1 , 3 )
( h , k )
Radius
2 v5 units
Diameter
4 v5 units
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Lets Graph a Circle!!!
Example (x 4)2 (y 2)2 16
(4, 2)
Center location
4 units
Radius
4
You cant fool us. Its not that easy!
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• (x h)2 (y k)2 r2
• Write the equation of the circle with
• endpoints (diameter) of (7, 3) and (5, 5)

The center of the circle is the midpoint of the
endpoints (diameter).
?
Center (6, 1)
Use the distance formula to find the radius
Radius
(x 6)2 (y 1)2 17
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Hang on! You said that we needed completing the
square for Conic Sections!
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What is the equation and graph of the circle x2
8x y2 6y 11 0
(-6 / 2)2 9
x2 8x y2 6y 11
16
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16
9
(8 / 2)2 16
(x 4)2 (y 3)2 36
Center (4, 3)
Radius 6
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I like circles!