X²﹢2X﹢Y²﹣8Y﹢17=0

(4x-2y-z)-{5x[8y-2y-(x+y)]-x+(3y-10z)]=4x-2y-z-5x[6y-(x+y)]+x-(3y-10z)=4x-2y-z-30xy+5x²+5xy+x-3

（x+2y)(x-2y)-(2y-x)(-2x-y)=（x+2y)(x-2y)+(x-2y)(-2x-y)=(x-2y）[(x+2y)+(-2x-y)]=(x-2y)(-x+y)代入x=8y=-8=-

[(x+2y)(x-2y)-(x-2y)^2+8y(x+y)]/4x=[x^2-4y^2-x^2-4y^2+4xy+8xy+8y^2]/4x=12xy/4x=3y

答：x-7y=0x=7y≠0所以：x/y=7,y/x=1/7(x²-3xy+y²)/(2x²﹢xy-3y²)=(x/y-3+y/x)/(2x/y+1-3y/x)

解13x-2y=9x-3y=2将式2左右两边同时乘以3得3x-9y=6与式1相减有-9y+2y=6-9解得y=3/7代入代2有x-3*3/7=2解得x=23/7故x=23/7y=3/7解2x+y=5x

根号(x+y-8)+根号(8-x-y)=根号(3x-y-4)+根号(x-2y+7),根据二次根式有意义得：X+Y-8≥0,8-X-Y≥0,∴X+Y≥8,X+Y≤8,∴X+Y=8,左边为0,右边两个非负

(x+y)/x=11/88x+8y=11y8x=3yy=8x/3(x-y)/(x+2y)=(x-8x/3)/(x+16x/3)=(-5x/3)/(19x/3)=-5/19

3x=8yx/y=8/3（1）x+y/y=x/y+1=8/3+1=11/3(2)2x+3y/x-2y分子分母同时除以y得=(2x/y+3)/(x/y-2)=(16/3+3)/(8/3-2)=(25/3

根据根号的双重非负性∴(x－3)≥0,(3－x)≥0∴x=3∴y=0+0+8=8x+3y=3+3×8=27∴x+3y的立方根为3

X=2,Y=3或X=3,Y=2

x²﹢y²-xy+2x-y+1=0关于Y的方程y^2-(x+1)y+(x+1)^2=0判别(x+1)^2-4(x+1)^2>=0-3(x+1)^2>=0,而(x+1)^2>=0所以

X+Y分之X-Y等于3x=-2yX+Y分之2(x-y)减X+Y分之3X+Y=(-x-3y)/(x+y)=1

因为(x-y)/(x+y)=3,则(x＋y)/(x－y)＝1/3则5(x-y)(x+y)-(x+y)/2(x-y)＝5*3-1/(3*2)=15-1/6=89/6

设所求的圆为：(x²﹢y²﹣x﹢y﹣2)+k(x²﹢y²-5)=0(1+k)x^2+(1+k)y^2-x+y-2-5k=0圆心为(1/2(1+k),-1/2(1

先一个一个的展开括号项,再同项合并就行了啊[x(x-y)-y(x-y)+(x+y)(x-y)]÷2x=[xx-xy-(xy-yy)+x(x-y)+y(x-y)]÷2x=[xx-xy-xy+yy+xx-

解9y=3x-(x-1)2x-9y+1=0①4(x+y)-(2x+4)=8y2x-4y-4=0②②-①得：5y-5=0∴y=1将y=1代入①得：2x-9+1=0∴x=4∴方程的解为：x=4,y=1

x+y/y=11/8说明11y=8（x+y）即8x=3y所以x-y/x+2y=3（x-y）/3(x+2y)=（3x-3y）/(3x+6y)=(3x-8x)/(3x+16x)=-5/19

基本不等式5分之2根号10

按照你的思路：2x+8y=xy2x+8y≥8√xy上式取“=”的条件是2x=8y即x=4y时,2x+8y取得最小值8√xy由此推出的xy≥8√xy--->√xy≥8--->2√xy≥16它取“=”的条

很累-3x-2y