1, addition, subtraction, multiplication and division all appear in the same formula. To calculate the addition and subtraction first, you must add parentheses.

2. There are addition and subtraction in an expression. If you need to calculate the following operations first, you must put parentheses.

There are multiplication and division in the expression. If you need to calculate the following operations first, you must put parentheses.

Function:

The function of changing the operation sequence. For mixed operations, the operation order should be considered, and the addition, subtraction, multiplication and division should be designated as first-level, second-level and third-level operations, and the operation order should be third-level, second-level and first-level. Sometimes in order to change the order of this operation, it is necessary to use parentheses to indicate the parenthetical prefix.

At the same time, it also stipulates the level of brackets, with braces as the outermost layer, braces containing brackets and brackets containing parentheses. When calculating, it is generally carried out in the order from inner brackets to outer brackets.

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