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Equations of circles
Contributed by: Smith
(Original author: Crouch)
(h,k)
(-3, 7)
center
r
(
(
(   +3)2+(   -7)2 =
(x+3)2 +(y-7)2 =
The CENTER, represented by point (h,K)
is where the LEFT side of the equation
is equal to zero.  Example below:
  (0)2  +   (0)2 =
-3
 Horizontal
   change
x-h
)
)
2
2
+
+
(
(
Vertical
change
y-k
7
)
)
2
2
=
=
radius2
r2
r2
r2
r2
What x and y  values make the left side of the equation
equal zero?
What is the center of the circle?
What is the radius of the circle?
r2
(x+2)2 +(y-5)2 =16
=16, use square roots to find r.
(
,
)
What x and y  values make the left side of the equation
equal zero?
What is the center of the circle?
What is the radius of the circle?
r2
(x+7)2 +(y+5)2 =16
=16, use square roots to find r.
(
,
)
What x and y  values make the left side of the equation
equal zero?
What is the center of the circle?
What is the radius of the circle?
r2
(x+12)2 +(y+35)2 =16
=16, use square roots to find r.
(
,
)
What x and y  values make the left side of the equation
equal zero?
What is the center of the circle?
What is the radius of the circle?
r2
(x-6)2 +(y-8)2 =25
=25, use square roots to find r.
(
,
)
What x and y  values make the left side of the equation
equal zero?
What is the center of the circle?
What is the radius of the circle?
r2
(x+2)2 +(y-5)2 =36
=36, use square roots to find r.
(
,
)
What x and y  values make the left side of the equation
equal zero?
What is the center of the circle?
What is the radius of the circle?
r2
x2 +(y-22)2 =9
=9, use square roots to find r.
(
,
)
What x and y  values make the left side of the equation
equal zero?
What is the center of the circle?
What is the radius of the circle?
r2
x2 +y2 =121
=16, use square roots to find r.
(
,
)
What x and y  values make the left side of the equation
equal zero?
What is the center of the circle?
What is the radius of the circle?
r2
(x+13)2 +(y-1)2 =64
=16, use square roots to find r.
(
,
)
What is the radius of the circle?
What x and y  values make the left side of the equation
equal zero?
r2
What is the center of the circle?
(x+13)2 +(y-1)2 =
=25/9, find the square roots of numerator and denominator
 SEPARATELY to find r.
(
,
25
)
9
What is the radius of the circle?
What x and y  values make the left side of the equation
equal zero?
r2
What is the center of the circle?
(x+3)2 +(y)2 =
=25/9, find the square roots of numerator and denominator
 SEPARATELY to find r.
(
,
49
81
)
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