已知xy是正实数,x方 y方=4
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5X方—3XY—4Y方—11XY—7X方+2Y方=-2x²-2y²-14xy=-2×7-14×(-2)=-14+28=14
A-B=4x^2-4xy+y^2-x^2-xy+5y^2=3x^2-5xy+6y^2
因为3x方+xy-2y方=0,即(x+y)(3x-2y)=0,而x+y≠0,所以3x-2y=0原式=[(x+y)^2-4xy]/[(x+3y)(x-y)/(x+3y)(x-3y)=(x-3y)/(x+
k=(y+2)/(x+1)所以k就是过点(-1,-2)的直线的斜率x,y满足x^2+y^2=1所以就是求过点(-1,-2)的直线和单位圆有公共点是斜率的取值范围显然相切时有最值y+2=kx+kkx-y
x方+4y方=4xyx²-4xy+4y²=0(x-2y)²=0x=2yx+2y/x=(2y+2y)/(2y)=2
即(3x-4y)(x+y)=03x=4y或x=-y若3x=4yy=3x/4则y²=9x²/16,xy=3x²/4原式=(3x²/4-3x²)/(9x&
∵y/x=3∴y=3x∴原式=(3x²-12x²+18x²)/(6x²-3x*3x+7*9x²)=9x²/(60x²)=3/20
再问:图片看不全再答: 能看到了吧?
∵x^2+y^2-2x+4y+5=0配方:∴(x-1)^2+(y+2)^2=0那么x-1=0且y+2=0所以x=1,y=-2∴(x^4-y^4)/(2x^2+xy-y^2)*(2x-y)/(xy-y^
xy^2=4x+2y=x+y+y≥3三次根号(xy^2)=3三次根号4
2(x+y)方-2=50-2=48
当x方+1=y方+4时取到最小值X用4-Y代可以做了
x+y=15两边平方x²+2xy+y²=225所以2xy=225-(x²+y²)=12xy=6所以原式=113-6=107
∵y分之x=5∴x=5y(4x²-5xy-6y²)分之(x²-2xy+3y²)=(100y²-25y²-6y²)分之(25y
1/(x^4)+4/(y^4)xy=1,所以y=1/x即y^4=1/(x^4)代入原式,得到1/(x^4)+4(x^4)再由重要不等式,得到1/(x^4)+4(x^4)≥2(根号)1/(x^4)·4(
等于-1或5解那式子可得(x-5y)(y+x)=0得x=5y或x=-y
x²+2xy-3y²=0(x+3y)(x-y)=0解得x=y或x=-3y又x,y为正数所以y=x;x=-3y舍(x²+xy+y²)/(x²-xy+y&
这个不是直接算x、y而是对多项式进行变形;5x方-3xy-4y方-11xy-7x方+2y方=(5-7)x²+(-3-11)xy+(-4+2)y²=-2x²-14xy-2y
8=1/a+1/b≥2√(1/ab)从而16≥1/(ab)ab≥16又8=x²+y²≥2xy于是xy≤4所以ab>xy
2X方-4XY+4Y方-6X+9=0(x^2-4xy+4y^2)+(x^2-6x+9)=0(x-2y)^2+(x-3)^2=0所以有x-2y=0,x-3=0即有x=3,y=x/2=3/2x*根号8Y=