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显示全部楼层 · 2013-1-20 19:59:22

27.A-2B+C=1/2x-2(x-1/3y2)+3/2x+1/3y21/2x-2x+2/3y2+3/2x+1/3y2经过化简=y228.（先化简后把x.y代入）原式=1/2x-2x+2/3y2-3/2x+1/3y2经过化简=-3x+y2把x=-2，y=2/3代入代数式-3×（-2）+（2/3）2=58/929.还是先化解再代入，可以求出将其化开得:
-x2+3x-7=-2530.去括号，化解，代入。格式向我一样就行，得出x2-3x-13=-47/9;一定要选我满意答案，我可是比别人都...

千问 · 2013-1-20 19:59:22

(1)
A=1/2x; B=x-y2/3; C=3x/2+y2/3 代入：A-2B+C=1/2x-2(x-y2/3)+3x/2+y2/3=y2(2) 将其化开得：-3x+y2=6+4/9=58/9(3)将其化开得:
-x2+3x-7=-25;(4)将其化开得...

千问 · 2013-1-20 19:59:22

27.A-2B+C=1/2x-2(x-1/3y2)+3/2x+1/3y21/2x-2x+2/3y2+3/2x+1/3y2经过化简=y228.（先化简后把x.y代入）原式=1/2x-2x+2/3y2-3/2x+1/3y2经过化简=-3x+y2把x=-...

千问 · 2013-1-20 19:59:22

A=1/2x; B=x-y2/3; C=3x/2+y2/3 代入：A-2B+C=1/2x-2(x-y2/3)+3x/2+y2/3=y2-3x+y2=6+4/9=58/9-x2+3x-7=-25 x2-3x-13=-47/9...

千问 · 2013-1-20 19:59:22

27:
A-2B+C
=1/2x-2(x-1/3y2)+3/2x+1/3y2
=1/2x-2x+2/3y2+3/2x+1/3y2
=2/3y2+1/3y2
=y2 28~30：
式子不复杂，直接把x，y代入原式就行...