解:①8+(﹣)﹣(﹣0.25) =8﹣0.25+0.25 =8 ②25×﹣(﹣25)×+25×(﹣)=25×(+﹣) =25 ③(2x2﹣xy)+(x2+xy﹣3)=(2+1)x2﹣xy+xy﹣3 =3x2﹣3 ④﹣8m2﹣[4m﹣2m2﹣(3m﹣2m2﹣7)] =(﹣8+2﹣2)m2﹣(4﹣3)m﹣7 =﹣8m2﹣m﹣7
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