Wordia - The Definition Of Circle
circle
noun, maths a closed plane curve every point of which is equidistant from a given fixed point, the centre. Equation: (x –h)2 + (y –k)2 = r2 where r is the radius and (h, k) are the coordinates of the centre; area πr2; circumference: 2πr
From Collins
©HarperCollins 2008. Collins English Dictionary definition of circle