This means that, using Pythagoras’ theorem, the equation of a circle with radius \(r\) and centre (0, 0) is given by the formula \(x^2+ y^2= r^2\). Find the equation of a circle with radius 3 ...

Image caption, The diameter is the whole distance across the circle, through its centre. The diameter is two radii. The radius is half of the diameter. The radius is the distance from the centre ...