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 ...

To work out the area of a circle: Find the value of the radius. If the diameter is given, this must be halved. Substitute the value of the radius into the formula for the area of a circle.