ELI5: Explain Like I'm 5

Jacobi's formula

Jacobi's formula is a math equation that helps us find the derivative of certain functions. You know when you learn about counting and you have to add numbers together? Well, when we use Jacobi's formula, we are doing something similar, but instead of adding numbers, we are adding functions.

To use Jacobi's formula, we need to know some things called partial derivatives. Don't worry, it's not as scary as it sounds. Partial derivatives are just like regular derivatives, but they help us find the rate of change of a function with respect to one of its variables, while holding all other variables constant.

So, let's say we have a function that has more than one variable, like this: f(x, y). We can use Jacobi's formula to find the derivative of our function with respect to x, which tells us how much our function changes if we change the value of x by a little bit.

Jacobi's formula looks like this: df/dx = (∂f/∂x) + (∂f/∂y) (dy/dx). Don't worry if it looks a little complicated, let's break it down.

The "df/dx" part on the left side of the equation represents the derivative of our function f with respect to x.

The "∂f/∂x" and "∂f/∂y" parts on the right side of the equation represent the partial derivatives of our function f with respect to x and y, respectively.

The "dy/dx" part on the right side of the equation represents the rate of change of the variable y with respect to x.

So, by adding the two partial derivatives multiplied by the rate of change of y with respect to x, we can find the derivative of our function f with respect to x.

Overall, Jacobi's formula helps us find the rate of change of a function that has more than one variable, which can be very useful in many different areas of math and science.