# Edexcel A Level

## Circles

##### Investigate Equation of Circle
A circle can be expressed with the cartesian equation $$\color{blue}{{\left( {x - a} \right)^2} + {\left( {y - b} \right)^2} = {r^2}}$$,
where a, b and r are constants.

The circle is centred at $$\color{blue}{(a, b)}$$ and has radius $$\color{blue}{r}$$.
##### Matching Circles
You can select eight green circles on this page. Using the sliders to match the blue dashed circle to the green circle will reveal the equation in each case, but can you say what the equation is before making the match?