Radius and Center
(h,k)=(,)
and r =
Diameter Points
A = (,)
B = (,)
Circle Equation
  

Evaluate the circle equation:
(x - 2)2 + (y + 5)2 = 81

This circle equation is in standard form:
(x - h)2 + (y - k)2 = r2

Determine h:

h = -1 * -2 = 2

Determine k:

k = -1 * +5 = -5

Determine center of the circle:

Therefore, our circle has a center (h, k) = (2, -5)

Determine radius:

Therefore, we have r2 = 81
r = ±√81
Since a radius is always positive
We have r = 9

General form of circle equation

Center (h, k) = (-2, +5) and r = r = 9:

Expand the standard form

x2 + y2 - 2hx - 2ky + h2 + k2 - r2 = 0

Plugg in our values for h,k, and r:

x2 + y2 - 2(-2)x - 2(+5)y + -22 + +52 - 92 = 0
x2 + y2 + 4x - 10y + 4 + 25 - 81 = 0

Combine our constants

x2 + y2 + 4x - 10y - 52 = 0

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