Most often in calculus, you deal with explicitly defined functions, which are functions that are solved for y in terms of x. In that case, finding the derivative is usually really simple, because you just call the left-side of the equation y', and then you differentiate the right side with respect to x.

But when you come across an implicitly defined function, finding the derivative isn't always that easy. Implicit functions are functions where the x and y variables are all mixed up together and can't be easily separated. That's when implicit differentiation comes in handy.

Implicit differentiation lets us take the derivative of the function without separating variables, because we're able to differentiate each variable in place, without doing any rearranging.

When we use implicit differentiation, we differentiate both x and y variables as if they were independent variables, but whenever we differentiate y, we multiply by dy/dx. That's because y, as a dependent variable, is actually a function of x. Therefore, when we take its derivative, it's as if we're taking the derivative of a composite function, and we therefore have to apply chain rule. When we do apply chain rule, we multiply by the derivative of y, which is dy/dx.

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