Multiple variable function error propagation

When we have $x_n$ with uncertainties $\delta_{x_n}$ the error of $f(x_1, … , x_n)$ can be approximated by:

$$ \delta_f = \sqrt{(\frac{\partial f}{\partial x_1}\delta_{x_1})^2 + … + (\frac{\partial f}{\partial x_n}\delta_{x_n})^2} $$ Source: https://courses.washington.edu/phys431/propagation_errors_UCh.pdf