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 ...

One method of obtaining this equation is to integrate dxdy over the area of a circle ... trick people used in the past to find the area under a curve on a graph (before technology gave us better ...