The absolute value mostly depends on what is in the absolute value. For example, if there is an unknown formula of X, first look at the definition domain and what is the value domain of X. If some questions look at the definition domain of the topic or X has its own definition domain, the absolute value can be directly removed. There are also some topics that are discussed in categories. When the formula in the absolute value is ≧0, the absolute value is directly removed without affecting the positive and negative of the formula inside. If the formula is less than 0, add a negative sign to the formula inside, and then remove the absolute value. . . That's all.