sin(α_{1}) = \frac{v_{1}Δt}{AB}

sin(α_{2}) = \frac{v_{2}Δt}{AB}

\frac{sin(α_{1})}{sin(α_{2})} = \frac{v_{1}}{v_{2}}

speed of wave v_{1} = \frac{v}{n_{1}}

\frac{sin(α_{1})}{sin(α_{2})} = \frac{n_{2}}{n_{1}}