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Explanation:
The center is the origin, so (h,k) = (0,0).
The point (x,y) = (2,6) is on the circle's edge. We'll use these four values to find the value of r^2
(x-h)^2 + (y-k)^2 = r^2
(2-0)^2 + (6-0)^2 = r^2
2^2 + 6^2 = r^2
4 + 36 = r^2
40 = r^2
r^2 = 40
We don't need to solve for r itself. If you wanted to, you'd get the radius to be r = sqrt(40) = 2*sqrt(10) = 6.324555 approximately.
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Since h = 0, k = 0, and r^2 = 40, we can say:
(x-h)^2 + (y-k)^2 = r^2
(x-0)^2 + (y-0)^2 = 40
x^2 + y^2 = 40
