Not just junior high school math books. In mathematics, as long as it is formal, a period is used. Not because of a mistake. Writing a math paper is also very important for us, that is, it can never end.

From other places:

A, China people * * * and People's Republic of China (PRC) national standards; (GB/T 15834- 1995) pointed out: "... there is another form of period, that is, the dot". ",which is generally used in scientific and technological literature. "

Second, for many years, the mathematics textbooks in middle schools and above in China have been used to expressing with periods. The reason may be that the period is easily confused with some symbols in mathematics (science and technology).

Three dots are used to indicate ellipsis, which is only used to omit numbers, letters, etc. If normal text is omitted, six dots are still used. This is the habit of China sci-tech editors, probably considering the usage of western languages.