Al and Curt live at opposite corners of a square lot; Beth and Dawn live at the other two corners. They all carry water from a spring located within the lot. The spring is feet from Al, feet from Beth, and feet from Curt. How far is the spring from Dawn?
Source: NCTM Mathematics Teacher 2008
Subtract Eq. (2) from Eq. (1)
Subtract Eq. (3) from Eq. (4)
Compare Eq. (5) and Eq. (6)