# Implicit differentiation

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 $\dfrac{dy}{dx}=-\dfrac{x}{y}$.