X+2Y=3 求X分之1加Y分之1的max
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1/x+1/y=2(x+y)/xy=2x+y=2xy(2x-xy+2y)/(3x+5xy+3y)=[2(x+y)-xy]/[3(x+y)+5xy]=(4xy-xy)/(6xy+5xy)=3xy/11x
分子分母同除以xy,分子变为2(1/x+1/y)+3=2x3+3=9分母变为(1/x+1/y)+2=3+2=5答案是9/5
x加y分之xy=1/[1/x+1/y]=1/[(√2+√3-3)/2+(√2+3-1)/2]=1/(√2+√3-2)
再问:2/5再答:?
你现在高一么?如果是,那就应该是印刷问题应该是4的y次方吧x=lg36/lg3,y=lg36/lg42/x+1/y=(2lg3+lg4)/lg36=1
x+y=-3x=-y-3xy=2(-y-3)y=2-y²-3y-2=0y²+3y+2=0(y+1)(y+2)=0y1=-1y2=-2一、当y1=-1时,x1=-2,根号y分之x加根
x/2=y/3=z/4=tx=2ty=3tz=4tx+y-z=1/122t+3t-4t=t=1/12x=1/6y=1/4z=1/3xyz=1/6*1/4/*1/3=1/72
直接设X=1,Y=0.5.带入后式得出10
1/x+1/y=-1/21/x*1/y=1所以由韦达定理1/x,1/y是方程x²+x/2+1=0的根判别式小于0所以无解再问:x分之一加y分之一=1,x乘y分之1=负2分之求x、y,谢谢,感
此题简单做法你直接可以设X=1,Y=0.5,使其满足前面的条件即可,带入后面分式,后面的式子中文表述不清,
用x分之3加y分之4乘以(x+y),然后化简,再用均值不等式就出来了……(3/x+4/y)乘(x+y)等于7+3y/x+4x/y然后由于x,y大于0,所以用均值不等式即可……
令2分之X=3分之y=4分之z=mX+Y+Z=2m+3m+4m=9mX+Y-Z=2m+3m-4m=m一比等于9
是椭圆x^2/a^2+y^2/b^2=1a^2=2b^2=3画出来是椭圆再问:厉害
原式=[(x+2y)/(x+y)]×[xy/(x+2y)]÷[(x+y)/xy]=[(x+2y)/(x+y)]×[xy/(x+2y)]×[xy/(x+y)]=x²y²(x+2y)/
3∵x/y=1/2∴y=2x故(x^2+2xy+y^2)/(x^2-xy+y^2)=(x+y)^2/(x^2-xy+y^2)=(x+2x)^2/(x^2-x·2x+4x^2)=9x^2/(3x^2)=
x/2=y/3=z/4=tx=2ty=3tz=4t(x+y-2z)/(2x-y)=(2t+3t-8t)/(4t-3t)=-2
因为1/x+1/y=-3所以(x+y)/xy=-3即x+y=-3xy所以(x-6xy+y)/(3x+2xy+3y)=(-3xy-6xy)/[3(x+y)+2xy)]=-9xy/(-9xy+2xy)=9
{3分之y减6分之x加1=3,2(x-2分之y)=3(x加18分之yy/3-(x+1/6)=32y-6x=19(1)2(x-y/2)=3(x+y/18)2x-y=3x+y/612x-6y=18x+y6
利用柯西不等式(2/x+4/y)(x+y)≥(√2+2)²当且仅当x=2+4√2且y=4+2√2时取等∵2/x+4/y=1∴(x+y)≥(√2+2)²=6+4√2即(x+y)≥6+