X=1,2,3 y=1,2,3求Z=X Y联合概率密度-搜答案-智慧作业帮

x=1/3y=1/2x-(x+y）+（x+2y)-(x+3y)+...-(x+13y)=6y-13y=-7y=-7/2=-3.5

2x-3y=0(1)3x-y-1=0(2)由（2）得y=3x-1(3)把y=3x-1代入(1)得2x-9x+3=0∴x=3/7把x=3/7代入（3）得y=2/7∴x=3/7y=2/7

∵1/x-1/y=3∴y-x=3xy2x+3xy-2y/x-y=2(x-y)+3xy/x-y=-6xy+3xy/-3xy=1

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

3x-4y/2x+y=1/26x-8y=2x+y4x=9yx/y=9/4

原试=-y-y-y.-y大概有50个-y所以答案是-50/3

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

y=(x)＋(3/x)≥2√3,等号取得的条件是：x=3/x,即：x=√3,由于本题中,x>2,则x=√3是取不到的；第二题是无法使用基本不等式.则此类问题一般利用函数单调性来解决.1、函数y=(x)

把4看成2^22^x=2^2（y-1）得出x=2（y-1）27^y=3^3y=3^（x+1)得出3y=（x+1）联立两个方程就可以解决啦y=-1x=-4x-y=-3

1/x+1/y=(x+y)/xy=5x+y=5xy2x-3xy+2y/-x+2xy-y=[2(x+y)-3xy]/[2xy-(x+y)]=(10xy-3xy)/(2x-5xy)=7xy/(-3xy)=

7y(x-3y)²-2(3y-x)³=7y(x-3y)²+2(x-3y)³=(x-3y)²[7y+2(x-3y)=(x-3y)²(7y+2X

x｛x-1｝-｛x＾2-y｝＝-3即x^2-x-x^2+y=-3-x+y=-3x-y=3而x＾2+y＾2-2xy=(x-y)^2=3^2=9

原式=(x-y)²-3(x-y)+1=3²-3×3+1x-y用3代替=1再问：3X+3Y是怎么转化成这个的3(X-Y)，什么理由再答：是-3x+3y不是3x+3y

y'=3-2xy'/x=1=1y'/x=0=3

y=2x2;-4x+2-3=2(x-1)2;-30≤x≤3-1≤x-1≤2所以0≤(x-1)2;≤40≤2(x-1)2;≤8-3≤2(x-1)2;-3≤5所以值域[-3,5]

把x=9y带入到3x=2y+1中得到3*(9y)=2y+127y=2y+125y=1y=1/25x=9y=9/25所以x=9/25,y=1/25

(x-2y)/(x+2y)=3取倒数(x+2y)/(x-2y)=1/3所以原式=(1/3)[(x-2y)/(x+2y)]-3[(x+2y)/(x-2y)]=(1/3)×3-3×(1/3)=0

-2x+3y=3x-2y+13y+2y=3x+2x+15y=5x+15y-5x=1y-x=1/5∴y＞x谢谢采纳满意请采纳

原式=x-x+x-x+……-x+(2-1+4-3+5-4+……+2008-2007-2009）y=0+(1×1004-2009)y=-1005y=1005/2