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How to do the problem of page 52 12 in the seventh grade math book?
1. Wrong, because -(0)=0.

2. Yes, because the root sign (the square of a) =+-a.

3. Wrong, because when a>0, b<0,1/A > 1/b, when a=0 or b=0, 1/a or 1/b is meaningless.

At least I have a wrong answer to the third question of happiness.