已知A=5x²y-3xy²+4xy；B=7xy²-2xy+x²y，且x+y=2，x-y=0，化简求-1/2（A+B)-A。
已知A=5x²y-3xy²+4xy；B=7xy²-2xy+x²y，且x+y=2，x-y=0，化简求-1/2（A+B)-A。
解
x+y=2
x-y=0
两式相加得：2x=2
∴x=y=1
-1/2(A+B)-A
=-1/2A-1/2B-A
=-3/2A-1/2B
=-3/2(5x²y-3xy²+4xy)-1/2(7xy²-2xy+x²y)
=(-15/2x²y-1/2x²y)+(9/2xy²-7/2xy²)+(-6xy+xy)
=-8x²y+xy²-5xy
=-8×1×1+1×1-5×1×1
=-8+1-5
=-12
已知A=5x²y-3xy²+4xy,B=7xy²-2xy+x²y 求A-2B
A-2B
=5x²y-3xy²+4xy-2(7xy²-2xy+x²y)=5x²y-3xy²+4xy-14xy²+4xy-2x²y=3x²y-17xy²+8xy答题不易 望采纳
化简求值(x+y)(x-y)-(x-y)²-6x²y/2y+(2xy)²/(-4xy)其中x=-2,y=1/3
(x+y)(x-y)-(x-y)²-6x²y/2y+(2xy)²/(-4xy)
=x²-y²-x²+2xy-y²-3x²-xy
=-3x²-2y²+xy
当x=-2,y=1/3时
原式=-12-2/9-2/3
=-12又8/9
4x²y-1/2{x²y-[5x²y-2(2xy²+1/4xy)]}+3xy²,其中x=2,y=-3
4x²y-1/2{x²y-[5x²y-2(2xy²+1/4xy)]}+3xy²
=4x²y-1/2{x²y-[5x²y-4xy²-1/2xy]}+3xy²
=4x²y-1/2{x²y-5x²y+4xy²+1/2xy}+3xy²
=4x²y-1/2{-4x²y-4xy²-1/2xy}+3xy²
=4x²y+2x²y+2xy²+1/4xy+3xy²
=6x²y+5xy²+1/4xy
=xy(6x+5y+1/4)
=-2×3×（6×2-5×3+1/4）
=-6×（-11/4）
=16.5
已知A=5x²-3y²+2xy,B=2x²+5y²-4xy,当x=1,y=-1时,求2A-5B的值
2A-5B
=2(5x²-3y²+2xy)-5(2x²+5y²-4xy)
=10x²-6y²+4xy-10x²-25y²+20xy
=-31y²+24xy
当x=1，y=-1时
原式=-31-24=-55
当x=-3,y=-4时,3x²y+[2xy²-(5x²y-3xy²)+4x²y]-xy=？
3x²y+[2xy²-(5x²y-3xy²)+4x²y]-xy
=2x²y+5xy²-xy
=xy(2x+5y-1)
=12x(-27)
=-324
化简求值 已知：（x+2）2;+|y+1|=0求5xy²-｛2xy²-[3xy²（4xy²-2x²y）]｝的值
（x+2）^2+|y+1|=0
x=-2，y=-1
5xy²-｛2xy²-[3xy²（4xy²-2x²y）]｝
= 5xy²-2xy²+3xy²(4xy²-2x²y)
= 3xy²+3xy²(4xy²-2x²y)
= 3xy²{1+2xy(2y-x)}
= 3*(-2)*(-1)^2 * { 1 + 2*(-2)*(-1)*[2*(-1)-(-2)]}
= -6 * { 1 + 0 }
= -6
化简求值2x²—5xy+2y²—x²—4xy—2y²
2x²—5xy+2y²—x²—4xy—2y²
=2x²—x²—5xy—4xy+2y²—2y²
=x²-9xy
化简求值：3(2X²Y-3XY²）-2（2XY²-3X²Y），其中X=1，Y=-1.17
3(2X²Y-3XY²）-2（2XY²-3X²Y）=6X²Y-9XY²-4XY²+6X²Y=12X²Y-13XY²，其中X=1，Y=-1.17
=12*(-1.17)-13(-1.17)(-1.17)=31.8357
3A²-2（2A²+A）+2（A²-3A）=3A²-4A²-2A+2A²-6A=A²-8A=4+16=20
