Doctors are able to treat kidney stones, which are hard deposits made of minerals and salts that form inside the kidneys, using a process called Extracorporeal Shockwave Lithotripsy (ESWL). Using this process, there is a lower risk of infectionand less recovery time is needed than if a patient undergoes surgery. A lithotripter is used to carry out this procedure.

The lithotripter machine contains half of an ellipse and uses one focus of the ellipse as the source ofshockwaves that reflect off of the surface of the ellipse. If kidney stones are located at the other focus of the ellipse, they arestruck by the shockwavesare broken up and fragmented into very small pieces that are more easily passed by the body.

A. Using the diagram below, place a dot where the kidney stones should be located in order to be successfully struck by the lithotripter machine.