The radius of a circle or a sphere is the distance between the center and the edge. The radius can be used to calculate a circle's diameter, area and circumference. Likewise, a sphere's volume is ...

To find the equation of a circle when you know the radius and centre, use the formula \({(x - a)^2} + {(y - b)^2} = {r^2}\), where \((a,b)\) represents the centre of the circle, and \(r\) is the ...