According to the algorithm, subtracting a number is equal to adding the inverse of this number, and the subtraction operation is unified as the addition operation. This change process is transformed into addition operation. Unified into addition, you can omit the plus sign to achieve the form of omitting the algebraic sum of the plus sign. such as

2-(-4)+36-4 1- 15

=2+4+36+(-4 1)+(— 15)

The form of omitting the sum of plus signs is algebraic sum.

2+4+36-4 1- 15

+3-(-2)

Because there is a negative number in brackets and a minus sign in front of it, it should become a plus sign. If there is a plus sign in front of the brackets, the bracket invariant symbol should be removed.