設隨機變量(x,y)的分佈律如表所示,求(x,y)的分佈函數-搜答案-搜搜做题作业网

x+x+x+y+y=54,x+x+y+y+y=56得出3X+2Y=54,2X+3Y=56扩大后得出6X+4Y=108,6X+9Y=118两式相减得出Y=2得出X=50/3

y/x=ty=txy'=t+x*dt/dx=t+1/tx*dt/dx=1/ttdt=dx/x然后再算

|x-y|=x-y>0x>y又|x|=1999|y|=2000x=-1999,y=-2000x+y=-3999

x^2=x的平方‘/’为除以[(x+2y)^2-(x+y)(x-y)-5y^2]/(2x)=[(x^2+4xy+4y^2)-(x^2-y^2)-5y^2]/(2x)=[4xy]/(2x)=2y[(3x

(x-y)的2次方-2(x-y)+(x-y)-5(x-y)=(x-y)²-2(x-y)+(x-y)-5(x-y)=(x-y)²-(x-y)-5(x-y)=(x-y)²-6

2(y-x)²-7(x-y)+6(x-y)-3(y-x)²=-(y-x)²-(x-y)=-(x-y)²-(x-y)=-(x-y)[(x-y)+1]=(y-x)(

(x-y)的四次方(x-y)-2(x-y)²(y-x）³=(x-y)的五次方+2(x-y)五次方=3倍(x-y)五次方

(x-y)(z+y-x+y+2y)÷4y=(x-y)(z-x+4y)÷4y{(x+y)(x-y)-(x-y)的2次方+2y(x-y)}除以4y=(x-y)(x+y-x+y+2y)÷4y=(x-y)(4

详见：http://hi.baidu.com/%B7%E3hjf/album/item/5fa110df8b26067395ee37a7.html

xyx+yyx+yxx+yxyc1+c2+c32(x+y)yx+y2(x+y)x+yx2(x+y)xyr3-r2,r2-r12(x+y)yx+y0x-y0-yy-x--此时用对角线法则得=2(x+y)

左式-右式=（x^3+xy^2-yx^2-y^3）-(x^3-xy^2+yx^2-y^3)=2xy^2-2yx^2=2xy(y-x)当x=0或y=0或x=y时,两式相等当y＞x＞0或x＜y＜0或y＜0

因为X-Y=1所以原式=x*1+y*（-1）+2013=x-y+2013=1+2013=2014

|x|+x+y=10|y|+x-y=12两式相加得|x|+|y|+2x=22.(1)两式相减得|x|-|y|+2y=-2.(2)所以-|y|+2y＜0若y＞0,则显然-y+2y＜0,即y＜0,矛盾若y

选B,A选取的是x,y的最小值；其他两个都不是.再问：能分析一下吗？再答：其实就是对C语言中的问号表达式的理解，我们拿B来理解一下：B.x

(x-y)平方+2y(x-y)=(x-y)(x-y+2y)=(x-y)(x+y)

x/(x+y)(x--)^3=x/(x+y)(x--y)^3y/(y+x)(y--x)^2=y(x--y)/(x+y)(x--y)^3.

解(x-y)(x+y)-(x-2y)²+x(3x-5y)-(x-y)(x-2y)=(x²-y²)-(x²-4xy+4y²)+(3x²-5xy

原式=(x+y)(x-y)(x^2+y^2)(x^4+y^4)=(x^2-y^2)(x^2+y^2)(x^4+y^4)=(x^4-y^4)(x^4+y^4)=x^8-y^8

x(x-y)²-(y-x)³=x(x-y)²+(x-y)³=(x-y)²[x+(x-y)]=(x-y)²(2x-y)