(1/2xy+y²+1)+(x²-1/2xy-2 y²-1)2.-(x²y+3xy-4)+3
题目
(1/2xy+y²+1)+(x²-1/2xy-2 y²-1)2.-(x²y+3xy-4)+3
(x²y-xy+2)3.-1/4(2k^3+4k²-28)+1/2(k^3-2k2+4k)求值:3x²-(2x²+5x-1)-(3x+1)其中x=10
(xy-3/2y-1/2)-(xy-3/2x+1)其中x=10/3,y=8/3;4y²-(x²+y)+(x²-4y²),其中x=-28,y=18.
答案
2.-(x²y+3xy-4)+3 (x²y-xy+2)
=-x^2y-3xy+4+3x^2y-3xy+6
=2x^2y-6xy+10
3. -1/4(2k^3+4k²-28)+1/2(k^3-2k2+4k)
=-1/2k^3-k^2+7+1/2k^3-k^2+2k
=-2k^2+2k+7
求值:3x²-(2x²+5x-1)-(3x+1)其中x=10
3x^2-2x^2-5x+1-3x-1
=x^2-8x
=10^10-8*10
=100-80
=20
(xy-3/2y-1/2)-(xy-3/2x+1)其中x=10/3,y=8/3
=xy-3/2y-1/2-xy+3/2y-1
=-3/2
4y²-(x²+y)+(x²-4y²),其中x=-28,y=18.
4y^2-x^2-y+x^2-4y^2
=-y
=-18
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