1, in order to express two quantities with opposite meanings (such as profit and loss, income and expenditure, etc.). ), learning 0, 1, 3.4, 2/5, etc. is not enough. So there is a negative number, the profit is positive and the loss is negative; Take income as positive and expenditure as negative.

2. If a number is less than 0, it is called a negative number.

There are countless kinds of negative numbers, including (negative integer, negative fraction, negative decimal).

4. Writing of negative numbers: There is a negative sign "-"in front of the number, which cannot be omitted. For example: -2, -5.33, -45, -2/5.

5. On the number axis, all negative numbers are on the left of 0. 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.