Question 746357: How do I write an equation for a circle whose center is (3,-1) and radius is 2? Found 2 solutions by savvyhush23, Edwin McCravy:Answer by savvyhush23(50) (Show Source):
You can put this solution on YOUR website! How do I write an equation for a circle whose center is (3,-1) and radius is 2?
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Which equation? the standard or the general equation?
In solving this problem, the standard equation is use:
Center is (3,-1) so h = 3 and k = -1, r^2 = 4 , this is the standard equation
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Simplifying, , this is the general equation of the circle.
You must memorize the standard equation of a circle
with center = (h,k) and radius = r
(x - h)² + (y - k)² = r²
In your problem center = (h,k) = (3,-1) and
radius = r = 2
So substitute (3) for h, (-1) for k and (2) for r.
DO NOT substitute anything for x or y, but leave them
variable:
(x - (3))² + (y - (-1))² = (2)²
(x - 3)² + (y + 1)² = 4
That's the answer in standard form. If you like you can
do some algebra on that and come up with the general form
x² + y² + Dx + Ey + F = 0
which will come out to be
x² + y² - 6x + 2y + 6 = 0
Edwin
