Mathematical Training of Lifeguards 
Proof
A reader familiar with trigonometric functions and basic elements of differential calculus, could try to prove the result we have just stated, at the end of the previous section. In the following application, we can see a geometric proof, that does not require a deep mathematical knowledge and that is, in fact, a natural extension of the arguments used in the previous particular case. 3
3 If you have Geogebra installed, you might prefer to import the applet from here and run it locally.
