# Dictionary:Law of tangents

${\displaystyle \rho _{1}\tan \alpha _{1}=\rho _{2}\tan \alpha _{2}}$
where ${\displaystyle \rho _{1}}$, ${\displaystyle \rho _{2}}$ are the resistivities of the two media and ${\displaystyle \alpha _{1}}$, ${\displaystyle \alpha _{2}}$ are the angles that the current flow makes with a normal to the interface.