You may be asked to show that two circles are touching, and say whether they're touching internally or externally. To do this, you need to work out the radius and the centre of each circle. If the sum ...

As a tangent is a straight line it is described by an equation in the form \(y - b = m(x - a)\). You need both a point and the gradient to find its equation. You are usually given the point - it's ...