# From the Chain Rule to Backpropagation

Learn how to apply chain rule in backpropagation.

## We'll cover the following

Backpropagation is an application of the **chain rule**, it is *one of the fundamental rules of calculus*. The chain rule calculates the gradient of any node y with respect to any other node $x$, we multiply the local gradient of all the nodes on the way back from $y$ to $x$.

Let’s understand how the chain rule works on a couple of network-like structures: a simple one, and a more complicated one.

## The chain rule on a simple network

Let’s look at this simple network-like structure:

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