化简或求值(本题满分16分,5+5+6):(1)2x2-2+3x-1-2x-x2; (2)a2-(3a2-b2)-3(a2-2b2)(3)已
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化简或求值(本题满分16分,5+5+6): (1)2x2-2+3x-1-2x-x2; (2)a2-(3a2-b2)-3(a2-2b2) (3)已知:(x-3)2+|y+2|=0,求代数式2x2+(-x2-2xy+2y2)-2(x2-xy+2y2)的值. |
答案
(1)2x2-2+3x-1-2x-x2 =x2+x-3; (2)原式=a2-3a2+b2-3a2+6b2 =-5a2+7b2; (3)∵(x-3)2+|y+2|=0, ∴x=3,y=-2, 2x2+(-x2-2xy+2y2)-2(x2-xy+2y2) =2x2-x2-2xy+2y2-2x2+2xy-4y2 =-x2-2y2 当x=3,y=-2时,原式=-17. |
举一反三
下列结果为负数的是( )A.-(-3) | B.-32 | C.(-3)2 | D.|-3| |
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