公元前6世纪,古希腊的毕达哥拉斯学派有一种观点：“万物皆数”,一切量都可以用整数或整数的比(分数)表示．后来,人们发现边长为1的正方形的对角线的长度2~(1/2)不能用整数或整数的比来表示,故称2~(1/2)为“无理数”．课本利用正方形作出了长为2~(1/2)的线段,并在数轴上作出了表示2~(1/2)的点A．如图1． In the 6th century BC, the Pythagorean school of ancient Greece had a view that “all things are counted”, and all quantities can be expressed as a ratio of integers or integers (fractions). Later, it was found that the length of the diagonal of the square with a side length of 1 can not be expressed as a ratio of integer or integer, so 2~(1/2) is called “irrational number”. The textbook uses squares to make a line that is 2~(1/2) long, and on the several axes, points A to 2~(1/2) are made. Figure 1.