y=30x (0.7x2 170x 10000)最小值

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

x+y=20-6=14x+y=14x=14-y3(14-y)+y=3042-3y+y=3042-2y=302y=12y=6x=8

6x-2y=21(1)18+2y+6x=30y所以6x-28y=-18(2)(1)-(2)6x-2y-6x+28y=21+1826y=39y=3/2x=(21+2y)/6=4

x(x-y)+y(y-x)=x(x-y)-y(x-y)=(x-y)(x-y)=(x-y)²明教为您解答,请点击[满意答案];如若您有不满意之处,请指出,我一定改正!希望还您一个正确答复!祝您

p(x+y)=PX+PY-P(XY)因为独立P(XY)=PXPYPX=0.5带入上式0.7=0.5+PY-0.5PY0.5PY=0.2PY=0.4再问：再问你一道，E(x)3,E(2x-3)=?再答：

x＋y＝450①0.4x﹣0.6y＝﹣30②①×0.40.4x＋0.4y＝180③③﹣②y＝210代入①x＝240即方程组的解为x＝240,y＝210,用几何方法表示是第一象限的点（240,210）

X=2,Y=3或X=3,Y=2

∵令y=xt,则y'=xt'+t代入原方程,得xt'+t=t/(t-1)==>xt'=(2t-t^2)/(t-1)==>(t-1)dt/(2t-t^2)=dx/x==>2dx/x+[1/t+1/(t-

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

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-

0.58=(0.5x+0.7y)/(x+y)0.58(x+y)=0.5x+0.7y0.58x+0.58y=0.5x+0.7y0.58x-0.5x=0.7y-0.58y0.08x=0.12yx：y=0.

应该是4x+2y=304x+y=22吧再问：��x��y�ֱ��Ƕ��١�再答：4x+2y=224x+y=30�ó�y=22-30=-8��y=-8���뵽4x+2y=22�еó�4x+��-16��

0.58=(0.5x+0.7y)/(x+y)0.58(x+y)=0.5x+0.7y0.08x=0.12yx/y=0.12/0.08=3/2

0.5x+0.7y=35x+0.4y=40化简,得5x+7y=350①5x+2y=200②①－②,得5y=150y=30将y=30代入①,得x=28.

5(x+y)+3(x-y)=908x+2y=901式5(x+y)-3(x-y)=302x+8y=302式1式乘以4-2式解得x=11y=1

（0.2x+0.1y）/2-（4x-y）/10=（x-y）/5+(3x+0.5y)/30①(3x+2y-1)/8=3-(0.8x-5y)/41②①两边同时乘以60得（6x+3y）-（24x-6y）=（

|x|+|y|=30①2|x|-3|y|=20②①*2-②得5|y|=40|y|=8①*3+②得5|x|=110|x|=22x=±22y=±8

假设：X=Y/XY=X/Y带入函数就是：F(y/x,x/y)=（y/x+x/y）/(y/x—x/y)=x²+y²)/(y²-x²)希望可以帮助你!

1.两边求导得：y'=-sin(x-y)(1-y')解得y'=sin(x-y)/[sin(x-y)-1]2.y'=-e^-xy''=e^-xy'"=-e^-x3.y'"=(e^2x)'"(sinx)+