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Six difficult problems in junior high school mathematics
1, positive number (as long as the absolute value is not 0, then the absolute value is positive.

2. Non-negative integers not greater than 4 are 0, 1, 2, 3; A nonnegative integer with an absolute value less than 3 is 0, 1, 2 (note that it is nonnegative); Integers greater than -3.5 and less than 3.2 are -3, -2,-1, 0, 1, 2,3.

3.a is a non-positive number (because when A

4. When A is nonnegative | a | = a When A is nonpositive | A | =-A.

5. By discussing the symbols of A, B and A+B, we know that | 2A |-A+B | may be A-B, 3A+B, -3A-B,-A+B; Any non-zero number has |x|/x=- 1 or 1, so |A|/A+|B|/B may be-2,0,2.

6. Because |x-2| and (y+2) 2 are both non-negative numbers and their sum is 0, they must all be 0, and x=2, y=-2 and x-y = 4 are obtained; Similar to A=- 1, B=2.