Question 798878
Did the centre and radius of the following circle: 
x^2 + y^2 = 2*r*x
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Did it what?
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x^2 - 2rx + y^2 = 0
x^2 - 2rx + r^2 + y^2 = r^2
(x-r)^2 + y^2 = r^2
The center is (r,0)
radius = r
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For any value of r, the center is on the x-axis and the circle tangent to the y-axis.