Analysis:

Addition and subtraction are first-order operations, and multiplication and division are second-order operations. If you can only calculate addition and subtraction or multiplication and division from left to right, if you have both addition and subtraction, multiply and divide first and then add and subtract, and the one in brackets is the first.

The mixed operation method of addition, subtraction and addition and subtraction;

1, the calculation method of continuous addition formula: from left to right; When calculating the seal type, it is relatively simple to list a vertical type.

2. Calculation method of continuous reduction formula: calculation is carried out from left to right; When the column is vertical, it can be written as vertical: you can do it directly without writing vertical.

3. Calculation method of addition and subtraction formula: from left to right; When the column is vertical, it can be written as two or one.

Extended data:

By using the properties of equations, the absolute value of the coefficient in front of an unknown number in two equations of equations is equal, and then the two equations are added or subtracted to eliminate the unknown number, so that the equation only contains one unknown number, and the solution can be obtained.

When the coefficients of an unknown number of two equations in the equations are equal or opposite, the two sides of the two equations are added or subtracted to eliminate the unknown number, so that the binary linear equation is transformed into a univariate linear equation, and finally the solution of the equations is obtained.

Using the basic properties of the equation, the coefficient of an unknown in the original equation group is transformed into the form of equal or opposite numbers.

Then, by using the basic properties of the equation, the two deformation equations are added or subtracted to eliminate an unknown number, and a one-dimensional linear equation is obtained (both sides of the equation must be multiplied by the same number, and it is forbidden to multiply only one side. If the unknown coefficients are equal, they will be subtracted, and if the unknown coefficients are opposite, they will be added). Solve this one-dimensional linear equation and find the value of the unknown quantity.

Baidu encyclopedia-addition, subtraction and elimination method