化简代数式的几道题3(x-1)-(x-5)2(x^2-y^2)-3(x^2-2y^2)(x+y)+3(x-y)-4(x+

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化简代数式的几道题

3(x-1)-(x-5)

2(x^2-y^2)-3(x^2-2y^2)

(x+y)+3(x-y)-4(x+y-2)

(2x^2-1+3x)-4(x-x^2+1)

-3a^2+(3a-5a^2)-1/2(4a^2+6a)

(8mn-3m^2)-5mn-2(3mn-2m^2)

3(2x^2-y^2)-2(3y^2-2x^2)

(8x^3-3x^2+3)-(9x^3-4x^2+5)

-(-4ab+b^2)-2(2ab-b^2)

辛苦了.

解
3(x-1)-(x-5)
=3x-3-x+5
=(3x-x)+(5-3)
=2x+2
2(x²-y²)-3(x²-2y²)
=(2x²-3x²)+(-2y²+6y²)
=4y²-x²
(x+y)+3(x-y)-4(x+y-2)
=(x+3x-4x)+(y-3y-4y)+8
=-6y+8
(2x^2-1+3x)-4(x-x^2+1)
=(2x²+4x²)+(3x-4x)+(-1-4)
=6x²-x-5
-3a^2+(3a-5a^2)-1/2(4a^2+6a)
=(-3a²-5a²-2a²)+(3a-3a)
=-10a²
(8mn-3m^2)-5mn-2(3mn-2m^2)
=(8mn-5mn-6mn)+(-3m²+4m²)
=-3mn+m²
3(2x^2-y^2)-2(3y^2-2x^2)
=(6x²+4x²)+(-6y²-3y²)
=10x²-9y²
(8x^3-3x^2+3)-(9x^3-4x^2+5)
=(8x³-9x³)+(-3x²+4x²)+(3-5)
=-x³+x²-2
-(-4ab+b^2)-2(2ab-b^2)
=4ab-b²-4ab+2b²
=b²

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