If we differentiate an implicit equation, this is called *implicit differentiation*.

For example, if \(x^2+y^2 = 4\), we can differentiate both sides with respect to \(x\), using the chain rule, and find that \[2x+2y\dfrac{dy}{dx}=0.\] This then rearranges to give \(\dfrac{dy}{dx}=-\dfrac{x}{y}\).