是《二次根式》一章的一个重要公式．学习了这一个公式以后，不少同学对它的正向运用比较得心应手，而对其逆闭却很不习惯．其实，有不少题目，逆用这一公式来解，可以化难为易，化繁为简，收到事半功倍之效．例1当x≠0时，把式子根号外面的因式移到报号里面，那么原式等于（） It is an important formula of the chapter “Secondary Roots”. After learning this formula, many students are more comfortable with its positive use, and are very unaccustomed to their closure. In fact, there are many problems that can be solved by using this formula to solve difficult problems, simplify the process, and get twice the result with half the effort. Example 1 When x ≠ 0, move the factor outside the root number of the expression to the report number, then the original expression is equal to ()