https://www.youtube.com/watch?v=JAf_aSIJryg&t=854s
https://www.youtube.com/watch?v=7dc6EYntb4g
A partial derivative is a derivative of a function of several variables, where one or more variables are held constant. In other words, it measures the rate at which the function changes as one of the variables changes while holding all other variables constant.
The partial derivative of a function f(x,y) with respect to x is denoted by ∂f/∂x
Similarly, the partial derivative of f(x,y) with respect to y is denoted by ∂f/∂y