Save guides, add subjects and pick up where you left off with your BBC account. To find the equation of a circle when you know the radius and centre, use the formula \({(x - a)^2} + {(y - b)^2} ...

You need both a point and the gradient to find its equation. You are usually given the point - it's where the tangent meets the circle. To find the gradient use the fact that the tangent is ...