2、(-98)-52=- 150;

3、42+(-9 1)=-49;

4、 12+(-74)=-62;

5. Addition and subtraction of positive and negative numbers means that the subtraction of two numbers with the same sign is equal to the subtraction of their absolute values, and the subtraction of two numbers with different signs is equal to the addition of their absolute values. Zero minus a positive number is a negative number, and zero minus a positive number. The addition of two numbers with different signs equals the subtraction of their absolute values, and the addition of two numbers with the same sign equals the addition of their absolute values. Zero plus positive equals positive, zero plus negative equals negative.

Extended data:

Introduction of negative numbers:

If all negative numbers are less than zero, then all negative numbers are less than positive numbers. Zero is neither positive nor negative. Then -a

A negative number is the reciprocal of its absolute value. On the number axis, negative numbers are all on the left of 0, and the earliest record of negative numbers is China's ancient mathematical work "Nine Chapters Arithmetic". In the calculation, it is stipulated that "positive calculation is red and negative calculation is black", that is, red calculation is used to represent positive numbers and black is used to represent negative numbers. Comparing the sizes of two negative numbers, the absolute value is larger but smaller.

Baidu encyclopedia-negative number