如果x y=4 3则3x 2y
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(1)4ab+8-2b2-9ab-6=-2b2-5ab+2(2)原式=3x2y-2x2y+6xy-3x2y+xy=-2x2y+7xy,当x=-1,y=-2时,原式=-2×(-1)2(-2)+7×(-1
xy+x2=xy2+xy2+x2≥33x4y24=3当且仅当xy2=x2时成立所以xy+x2的最小值为3故选A.
因为A+B+C=x3-2y3+3x2y+xy2-3xy+4+y3-x3-4x2y-3xy-3xy2+3+y3+x2y+2xy2+6xy-6=1,所以,对于x、y、z的任何值A+B+C是常数.
原式=2x2y+2xy-3x2y-3xy-4x2y=-5x2y-xy当x=-2,y=12时,原式=-9.
∵x+y=6,xy=4,∴x2y+xy2=xy(x+y)=4×6=24.故答案为:24.
根据题意得:(3x2y-2xy2)÷(-3x+2y)=-xy,则m=-xy.故选B.
∵xy<0,由二次根式的有意义,得y>0,∴x<0,∴原式=x2y=-xy.
原式=4x2y-6xy+3(4xy-2)+x2y+1=5x2y+6xy-5当x=2,y=-12时,原式=5×4×(-12)+6×2×(-12)-5=-21.
∵xy+x+y+7=0  
那个2是平方吧?可以用^代替原式=x^y+xy^=xy(x+y)=-3*6=-18
∵x+y=0,xy=-7,∴①x2y+xy2=xy(x+y)=-7×0=0;②x2+y2=(x+y)2-2xy=14.
∵2x+y=4,xy=3,∴2x2y+xy2=xy(2x+y)=3×4=12.故答案为:12
原式=y(x2+2x+1)=y(x+1)2,故答案为:y(x+1)2.
∵x+y=5,xy=6,∴x2y+xy2=xy(x+y)=5×6=30.故答案为:30.
x2y+xy2=xy*(x+y)因为x+y=-(7+xy)又x+y=(9+2xy)\3所以(9+2xy)\3=-(7+xy)3+2xy\3=-7-xy5xy\3=-10解得xy=-6所以x+y=-(7
由题意得(x-2)平方+(y-2)平方+(x-y)平方=0,故x=y=2,故x平方y=8
原式=2x2y+2xy-3x2y+3xy-4x2y=-5x2y+5xy,当x=-1,y=1时,原式=-5×(-1)2×1+5×(-1)×1=-5-5=-10.
原式=-xy(x-y),当x-y=3,xy=-2时,则原式=-3×(-2)=6.故答案为:6.
由题意得:3C=A+B=8x2y-6xy2-3xy+7xy2-2xy+5x2y=13x2y+xy2-5xy,∴C=13x2y+xy2−5xy3,故:C-A=13x2y+xy2−5xy3-(8x2y-6
解;∵x+y=0,xy=-7∴x2y+xy2=xy(x+y)=-7×0=0x2+y2=(x+y)2-2xy=02-2×(-7)=0+14=14.