The calculation of recursive equation should be: ① write the equal sign directly in one step, ② calculate in two steps, ③ calculate twice or more. The above three calculation methods are all recursive equations.

The recursive calculation method is: in the formula of elementary arithmetic, the calculation process is expressed by equations in turn according to the operation order, and such equations are called recursive equations.

In the same level operation, recursion needs to be calculated from left to right in turn, while in the two-level operation, multiplication and division are needed first, and then addition and subtraction are needed. Pay attention when special symbol brackets appear. If there are multiple brackets, please remember the bracket level clearly, first calculate the brackets, then the braces, and finally the exponent. Remember to calculate the index from high to low according to the operation level.