## Precalculus (6th Edition) Blitzer

With a known boat speed and an angle measuring device, at $t=0$, measure the angle of the lighthouse with respect to the boat path. After some time interval $\Delta t$, measure the angle again. The distance traveled will be the product of speed and time. Thus, with known $ASA$, we can solve the triangle, which gives the distance from the boat to the lighthouse.