在初中《代数》第二册“二次根式”这一章的复习与小结中有这样一句话:为了减少学习的困难,我们规定:“在本章中如果没有特别说明,根号内所有字母都表示正数,但是今后我们学习中遇到的二次根式,根号内的字母是可能取负值的。”教材中对根号内字母的取值作出这样的规定,有利于我们能够集中精力首先学好根 In the review and summary of the chapter “Secondary Roots” in the second edition of “Algebra” in the junior middle school, there is such a sentence: In order to reduce learning difficulties, we provide: “If there is no special explanation in this chapter, all letters in the root number are It means positive numbers, but in the future, we will encounter secondary root patterns, and the letters in the root number may take negative values." The provision of such a provision for the value of the letters in the root number in the teaching materials is conducive to the concentration of energy. First learn the root