搜狗做题网X Y=30 X-Y=20 2(X-2Y)-132
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x-xy=8(1)xy-y=-9(2)则有(1)-(2):X-XY-XY+Y=X+Y-2XY=8-(-9)=17
因为f（x+y,xy）=x^2+y^2=（x+y）^2-2xy所以f（x,y）=x^2-2y现对x求导得到：fx(x,y)=2x再对y求导得到：fxy(x,y)=0.所以无论x,y为何值,fxy(x,
原式=(x-y)(x²+2xy+y²-xy)-(x-y)(x²-2xy+y²+xy)=(x-y)(x²+xy+y²)-(x+y)(x&sup
题有问题吧,是X+XY+Y=14吧?如果是的话x+xy+y+y+xy+x=42合并一下（X+Y）+x+y=42设x+y=a则a+a=42a=6或a=-7
x^2+xy+y=14y^2+xy+x=28两式相加x^2+y^2+2xy+x+y=42(x+y)^2+(x+y)-42=0(x+y-6)(x+y+7)=0x+y=6或x+y=-7
Solution:x^2-2xy+3y^2=9(1)4x^2-5xy+6y^2=30(2)Eq(1)*5-Eq(2)*2,wehavex^2-y^2=5(3)Eq(2)-Eq(1),wegetx^2+
（x-y）[(x+y)(x+y)-xy]+(x+y)[(x-y)(x-y)+xy]=(x-y)(x+y)^2-（x-y)xy+(x+y)(x-y)^2+(x+y)xy=(x-y)(x+y)(x+y+x
(-3x^y+2xy)-(4x^+xy)=-3x^y+2xy-4x^-xy=-3x^y+xy-4x^所以填上-3x^y+xy-4x^
你确定没写错题目?后面的式子一约就变成前面的式子了,答案也是8/xy再问：怎么个约法?再答：y/xyyy约掉剩下1/x
x、y都是整数吧?就按这个解答.方程化为(x-1)(y+1)=17,由于17=1*17=(-1)*(-17),且x、y都是整数,因此可得（1）x-1=1,y+1=17,解得x=2,y=16；（2）x-
即(x-2y)²=0x-2y=0所以x=2y所以原式=(2x²+2xy-xy-y²)/(4x²-4xy+y²)=(2x²+xy-y²
7或者-8再问：求过程^_^再答：两个等式两边相加
2(x+xy)-[(xy-3y)-x]-(-xy)=2x+2xy-xy+3y+x+xy=3x+3y+2xy=3（x+y）+2xy=3*（-2）+2*3=0
∵x-y=4xy，∴2x+3xy-2yx-2xy-y=2(x-y)+3xyx-y-2xy=8xy+3xy4xy-2xy=112．故答案为：112．
xy+1/xy>=2√（xy*1/xy）=2(当xy=1/xy即xy=1时取等号)x/y+y/x>=2√（x/y*y/x）=2(当x/y=y/x即x=y取等号)当x=y=1时可以同时满足两项的等号要求
X²+2xy+y²/xy乘x²-2xy+y²/xy+y²=(x+y)²/xy×(x-y)²/y(x+y)=(x+y)(x-y)&#
由题意x,y为方程x^2-2009x-2010=0的2个根则x=2010,y=-1或者或者x=-1,y=2010
令y=kxx*x+kx*x=k*x+k*k*x*x(1-k*k+k)x^2-kx=0x((1-k*k+k)x-k)=0由上式得X=0或(1-k*k+k)x-k=0解得：k=(x-1+（或-）√（（1-
xy>0得x,y同号又因为x+y
x+2y+xy=30?x+2y≥2√(x×2y)=2√2√(xy)30=x＋2y＋xy≥2√2√(xy)+xy所以xy+2√2√(xy)-30≤0,令a=√(xy),显然a≥0：a²+(2√