x y=68 3%x 2.5%y=1.91
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解题思路:由完全平方公式可求解题过程:varSWOC={};SWOC.tip=false;try{SWOCX2.OpenFile("http://dayi.prcedu.com/include/rea
xy/x+y=1/3x+y=3xyx2y2/x2+y2=1/5(xy)²/[(x+y)²-2xy]=1/5(xy)²/[(3xy)²-2xy]=1/5(xy)&
x-y=1,(x-y)^2=x^2+y^2-2xy=12xy=25-1=24,xy=12(x+y)^2=x^2+y^2+2xy=25+24=49x^2-xy+y^2=25-12=13
设x2-xy+y2=Ax2-xy+y2=A与x2+xy+y2=1相加可以得到:2(x2+y2)=1+A(1)x2-xy+y2=A与x2+xy+y2=1相减得到:2xy=1-A(2)(1)+(2)×2得
∵x²-2xy-3y²=0∴*(x-3y)(x+y)=0∴x=3y或x=-y(1)2x+y/x-2y当x=3y时,原式=7y/y=7当x=-y时,原式=y/(-3y)=-1/3(2
X²(X+1)-Y(XY+X)=X^3+X²-XY²-XY=X^3-XY²+X²-XY=X(X²-Y²)+X(X-Y)=X(X-Y
x^2+2x+1+y-4根号y+4=0(x+1)^2+(根号y-2)^2=0x+1=0,根号y-2=0x=-1,y=4题目好像打错了
X^2+2Y^2-2XY-2Y+1=0X^2-2XY+Y^2+Y^2-2Y+1=0(X-Y)^2+(Y-1)^2=0因为两个数的平方为一个非负数,所以得:X-Y=0Y-1=0所以:X=1Y=1所以:X
x2+xy+y=1x2+xy+x=6两个相减得x-y=5x=5+y代入任何一个式子,可以得y=-2,-6x=3,-1
(1)A-2B=2x2+3xy+2y-1-2(x2−xy+x−12)=2x2+3xy+2y-1-2x2+2xy-2x+1=5xy+2y-2x,当x=y=-2时,A-2B=5xy+2y-2x=5×(-2
x(x-1)-(x2-y)=-3x2-x-x2+y=-3-x+y=-3所以x-y=3所以原式=(x-y)2=9
解题思路:完全平方公式解题过程:varSWOC={};SWOC.tip=false;try{SWOCX2.OpenFile("http://dayi.prcedu.com/include/readq.
∵x2+xy=5,xy+y2=-1,∴(x2+xy)-(xy+y2)=x2+xy-xy-y2=x2-y2=5-(-1)=6.故填:6
因为x2+y2=5,xy=2所以(x+y)^2=9x+y=+/-3所以1/(1/x+1/y)=xy/(x+y)=+/-2/3
(1)∵A=2x2+3xy+2y-1,B=x2-xy+x-12,x-y=-1,xy=1,∴A-2B=(2x2+3xy+2y-1)-2(x2-xy+x-12)=2x2+3xy+2y-1-2x2+2xy-
x²-2xy+y²/x²-y²=(x-y)²/(x-y)(x+y)=(x-y)/(x+y)因为x=3,y=-5,所以(3-(-5))/(3+(-5))
x^2+y^2=5;x^2-2xy+y^2=1;2/xy/[(1/x)-(1/y)]=-2;最后得到值为1
由x2+xy+y2=3得,x^2+y^2=3-xyx^2+y^2≥2xy得,xy≤1所以x^2-xy+y^2=3-2xy≥1等号成立当且仅当x=y=±1
原式=2x2-2xy-6x2+9xy-2x2+2x2-xy+y2=-2x2+5xy+2y2,当x=-1,y=-2时,原式=-2+10+8=16.
因为x²+4y²+x²y²-6xy+1=0(x²-4xy+4y²)+(x²y²-2xy+1)=0(x-2y)²