A little math challenge!

Here’s a little math for you amid all this turtle business. Today I helped triangulate a nest of eggs that was laid last night. This is how the process works. We first located the nest on the beach which was marked with sticks last night. Every 500m along the beach , at the vegetation line on the beach, are markers. From nest we took and recorded 3 measurements. The first measurement was to the nearest beach marker to the south of us, the second measurement to the nearest beach marker to the north of us and the third measurement was straight into the vegetation at the edge of the beach, perpendicular to the shoreline. Later we used previously recorded measurements to locate older nests. My challenge to you is how do we use these measurements in reverse to locate the nests and why is it called triangulation. This is simple Geometry girls!