Rule of rational number subtraction: subtracting a number is equal to adding the reciprocal of this number. Among them: two changes: subtraction becomes addition, and subtraction becomes its inverse. Invariant: The minuend is invariant. It can be expressed as: A-B = A+(-B).

Example:

Example 1 calculation: 1, (-3)-(-5)= 2, 0-7= 3, 7.2-(-4.8)= 4, 0-(-8)= Example 2: A, B, C, D on the number axis represent. (1)A and B. (2)C and D. (3)A and D. (4)O and c points. The highest mountain in the world is Mount Qomolangma, which is about 8844 meters above sea level, and the Turpan Basin is about-155 meters above sea level. What's the difference between two heights? Solution: 8844-(1 55) = 8844+155 = 8999 (m) Answer: The difference between the two heights is 8999 m (emphasizing the problem-solving format)1. Classroom exercise: 1. Is there a problem of "insufficient subtraction" when two rational numbers are subtracted? Is the difference necessarily less than the minuend? 2. If two numbers A and B are subtracted and the difference is negative, then A

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