X+Y=7,XY=2求2X的平方+2Y的平方:(X-Y)的平方
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已知x/y=7/2,(2x²+3xy+2y²)/(x²+2xy+y²)=(2x/y+3+2y/x)/(x/y+2+y/x)=(2×7/2+3+2×2/7)/(7
由X+Y=3XY可得X+Y-XY=2XY,用X+Y-XY替换分母中的2XY,所以(2X+2Y-XY)/(X+Y+2XY)=(2X+2Y-XY)/(2X+2Y-XY)=1
x-xy=8(1)xy-y=-9(2)则有(1)-(2):X-XY-XY+Y=X+Y-2XY=8-(-9)=17
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
根据题意得:分母:x+y+2xy=3xy+2xy=5xy分子:2x+2y-xy=2×3xy-xy=6xy-xy=5xy∴值为5xy分之5xy即为1
因为x-y=4xy所以x-2xy-y=2xy2x+3xy-2y=11xyx-2xy-y分之2x+3xy-2y=5.5
原式=6x+4xy+2xy+3x+2y-4xy+7y=9x+9y+2xy=9(x+y)+2xy=9×4+2×2=36+4=40
x+y=3xy,所以2x+2y-xy/x+y+2xy=(2×3xy-xy)/(3xy+2xy)=5/5=1
3xy-5=x+y>=2√(xy)3xy-2√(xy)-5=(3√(xy)-5)(√(xy)+1)>=0√(xy)>0所以√(xy)>=5/3xy>=25/9最小值25/9xy=(2+√19)/3最小
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
解题方法:分子、分母同时除一个xy(y+xy-x)/(2x+7xy-2y)=[(y+xy-x)/xy]/[(2x+7xy-2y)/xy]=(1/x+1-1/y)/(2/y+7-2/x)=[(1/x-1
(y+xy-x)/(2x+7xy-2y)(分子、分母同除一个xy)=(1/x+1-1/y)/(2/y+7-2/x)=6/(-10+7)=-2
3/5再问:详细过程呢再答:y-x=3xyx-y=-3xy代入得:(-6xy+3xy)/(-3xy-2xy)=-3/-5=3/5
(5xy+4x+7y)+(6x-3xy)-(4xy-3y)=5xy+4x+7y+6x-3xy-4xy+3y=(5xy-3xy-4xy)+(4x+6x)+(7y+3y)=-2xy+10x+10y=-2x
求x的平方y+xy的2次方=xy(x+y)=30
x(x-1)-(x^2-y)=5化简得y-x=5(y-x)^2=25y^2+x^2-2xy=25
∵x-y/xy=3∴x-y=3xy2x+3xy-2y/x-2xy-y=[2(x-y)+3xy]/[(x-y)-2xy]=(6xy+3xy)/(3xy-2xy)=9xy/(xy)=9
这类题,先化简代数式为XY与X+Y的代数式,然后代入已知条件,就可以算出来.(3xy+10y)+[5x-(2xy+2y-3x)]=3XY+10Y+5X-2XY-2Y+3X=XY+8Y+8X=XY+8(
(3x-2y+8xy)-(x-4y-5xy)=3x-2y+8xy-x+4y+5xy=(3x-x)+(-2y+4y)+(8xy+5xy)=2x+2y+13xy=2(x+y)+13xy=2×3+13×(-
x²-7xy+12y²=0(x-3y)(x-4y)=0x1=3yx2=4yx=3y时原式=9y²-3y²+y²/6y²=7/6x=4y时原式