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计算：⑴(3a^2-ab+7)-(-4a^2-2ab+7) (2)3xy-5xy-(-2xy)(3)(-x^2+5+4x

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计算：
⑴(3a^2-ab+7)-(-4a^2-2ab+7) (2)3xy-5xy-(-2xy)
(3)(-x^2+5+4x)+(5x-4+2x^2),其中x=-2
计算：⑴(3a^2-ab+7)-(-4a^2-2ab+7) (2)3xy-5xy-(-2xy)(3)(-x^2+5+4x
1 ,(3a^2-ab+7)-(-4a^2-2ab+7)
=3a^2-ab+7+4a^2+2ab-7
=7a^2+ab
2)3xy-5xy-(-2xy)
=3xy-5xy+2xy
=0
3)(-x^2+5+4x)+(5x-4+2x^2)
=-x^2+5+4x+5x-4+2x^2
=x^2+9X+1
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