计算或化简:
①;
②;
③;
④﹣12006﹣(1﹣0.5)×[3﹣(﹣3)2];
⑤3x2y﹣4xy2﹣3+5x2y+2xy2+5;
⑥3(2x2﹣y2)﹣2(3y2﹣2x2);
⑦先化简再求值:﹣2y3+(2x3﹣xyz)﹣2(x3﹣y3+xyz),其中x=1,y=2,z=﹣3.
解:①原式=﹣﹣﹣
=﹣1;
②原式=4﹣(﹣2)×3×(﹣3)
=4﹣18
=﹣14;
③原式=﹣÷(﹣)
=;
④原式=﹣1﹣××(﹣6)
=﹣1+1
=0;
⑤原式=8x2y﹣2xy2+2;
⑥原式=6x2﹣3y2﹣6y2+4x2
=10x2﹣9y2;
⑦原式=﹣2y3+2x3﹣xyz﹣2x3+2y3﹣2xyz
=﹣3xyz;
当x=1,y=2,z=﹣3时,原式=﹣3×1×2×(﹣3)=18.
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