求代数式2(a-2b)^2-3(2a+b)+5(a-2b)^2-(b+2a)的值,其中a=-1,b=2分之1有这样一道题:“当x=-2007,y=2008时,求多项式7x^3-6x^3y+3x^2y+3x^3+6x^3y-3x^2y-10x^3的值,求这个值”
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![求代数式2(a-2b)^2-3(2a+b)+5(a-2b)^2-(b+2a)的值,其中a=-1,b=2分之1有这样一道题:“当x=-2007,y=2008时,求多项式7x^3-6x^3y+3x^2y+3x^3+6x^3y-3x^2y-10x^3的值,求这个值”](/uploads/image/z/1642251-3-1.jpg?t=%E6%B1%82%E4%BB%A3%E6%95%B0%E5%BC%8F2%28a-2b%29%5E2-3%282a%2Bb%29%2B5%28a-2b%29%5E2-%28b%2B2a%29%E7%9A%84%E5%80%BC%2C%E5%85%B6%E4%B8%ADa%3D-1%2Cb%3D2%E5%88%86%E4%B9%8B1%E6%9C%89%E8%BF%99%E6%A0%B7%E4%B8%80%E9%81%93%E9%A2%98%3A%E2%80%9C%E5%BD%93x%3D-2007%2Cy%3D2008%E6%97%B6%2C%E6%B1%82%E5%A4%9A%E9%A1%B9%E5%BC%8F7x%5E3-6x%5E3y%2B3x%5E2y%2B3x%5E3%2B6x%5E3y-3x%5E2y-10x%5E3%E7%9A%84%E5%80%BC%2C%E6%B1%82%E8%BF%99%E4%B8%AA%E5%80%BC%E2%80%9D)
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求代数式2(a-2b)^2-3(2a+b)+5(a-2b)^2-(b+2a)的值,其中a=-1,b=2分之1有这样一道题:“当x=-2007,y=2008时,求多项式7x^3-6x^3y+3x^2y+3x^3+6x^3y-3x^2y-10x^3的值,求这个值”
求代数式2(a-2b)^2-3(2a+b)+5(a-2b)^2-(b+2a)的值,其中a=-1,b=2分之1
有这样一道题:“当x=-2007,y=2008时,求多项式7x^3-6x^3y+3x^2y+3x^3+6x^3y-3x^2y-10x^3的值,求这个值”
求代数式2(a-2b)^2-3(2a+b)+5(a-2b)^2-(b+2a)的值,其中a=-1,b=2分之1有这样一道题:“当x=-2007,y=2008时,求多项式7x^3-6x^3y+3x^2y+3x^3+6x^3y-3x^2y-10x^3的值,求这个值”
当a=-1,b=2分之1
2(a-2b)^2-3(2a+b)+5(a-2b)^2-(b+2a)
=7(a-2b)^2-4(b+2a)
=7(-1+1)^2-4(1/2-2)
=-4(-3/2)
=6
当x=-2007,y=2008时,
多项式7x^3-6x^3y+3x^2y+3x^3+6x^3y-3x^2y-10x^3
=(7x^3+3x^3-10x^3)+(-6x^3y+6x^3y)+(3x^2y-3x^2y)
=0+0+0
=0
不是全部抵消,最后等于0吗????