Find the equation of a circle with radius 3 units and centre (0, 0). The radius, \(r = 3\) and \(r^2 = 9\), so the equation of the circle is \(x^2 + y^2 = 9\). What is the radius of the circle given ...

A tangent to a circle at point P is a straight line that touches the circle at P. The tangent is perpendicular to the radius which joins the centre of the circle to the point P. As the tangent is a ...