All you do is cover up the path of the equation of the thing you want to find out, and the triangle shows you the right formula to use. Give it a go. When bats fly they make high frequency squeaks. These are reflected from objects as echoes. These echoes allow the bat to find out what is around them.
Bats have very poor eyesight but extremely large ears.
The diagrams show the wave trace of the bat's squeak and the echo from the wall. Compare the two traces. A company makes jet engines. The people living near the company complained about the noise from the engine test area, so it agreed to build an earth mound between the test area and the local village. The noise level was measured before and after the mound was built.