题目
合并同类项,
3x^2-[7x-(4x-3)-2x^2] 光求值：1/2x-2(x-1/3y^2)+(-3/2x+1/3y^2)其中x=-2,y=2/3 .3y^4-4x^3y+0.2x^2y^2-4y^4+0.5x^3y-1/5x^2y^2其中x=-2,y=0.3
3x^2-[7x-(4x-3)-2x^2] 光求值：1/2x-2(x-1/3y^2)+(-3/2x+1/3y^2)其中x=-2,y=2/3 .3y^4-4x^3y+0.2x^2y^2-4y^4+0.5x^3y-1/5x^2y^2其中x=-2,y=0.3
提问时间：2021-03-27
答案
3x^2-[7x-(4x-3)-2x^2]
=3x^2-[7x-4x+3-2x^2]
=3x^2-7x+4x-3+2x^2
=5x^2-3x-3
1/2x-2(x-1/3y^2)+(-3/2x+1/3y^2)
=1/2x-2x+2/3y^2-3/2x+1/3y^2
=-3x+y^2 x=-2,y=2/3
=-3*(-2)+4/9
=6+4/9
=59/9
3y^4-4x^3y+0.2x^2y^2-4y^4+0.5x^3y-1/5x^2y^2
=-y^4-3.5x^3y x=-2,y=0.3
=-0.0081-3.5*(-8)*0.3
=-0.0081+8.4
=8.3919
=3x^2-[7x-4x+3-2x^2]
=3x^2-7x+4x-3+2x^2
=5x^2-3x-3
1/2x-2(x-1/3y^2)+(-3/2x+1/3y^2)
=1/2x-2x+2/3y^2-3/2x+1/3y^2
=-3x+y^2 x=-2,y=2/3
=-3*(-2)+4/9
=6+4/9
=59/9
3y^4-4x^3y+0.2x^2y^2-4y^4+0.5x^3y-1/5x^2y^2
=-y^4-3.5x^3y x=-2,y=0.3
=-0.0081-3.5*(-8)*0.3
=-0.0081+8.4
=8.3919
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