Have you ever watched the long， curving flight of a baseball<br >home run? How fast would that baseball have to leave the<br >bat in order to travel a mile or several kilometers?<br > Normally， such questions are answered using mathe-<br >matics rather than by performing experiments. Experi-<br >ments can be great fun. But questions of this nature are<br >often asked out of intellectual curiosity. This kind of<br >curiosity is not so much about baseball as about thinking，<br >that is， curiosity about the way people solve puzzles.<br > The fun in asking such imaginative questions is not<br >really diminished because no player may ever actually hit a<br >baseball a mile. The novelty of asking the question and the<br >excitement of discovering a logical answer by thinking is<br >enjoyable in itself without actually trying to find a way to<br >hit a baseball such an unlikely distance.<br >FORMULA FACTS<br >Solving complicated problems often involves using mathe-<br >matical formulas， or equations. The formulas may come<br >from algebra， geometry， trigonometry， or some other<br >branch of mathematics. In many cases， a formula is used as<br >a rule， explaining how to evaluate some variable or quanti-<br >ty. To mathematicians and scientists， the term evaluate<br ><br >