xy=x-e的xy次-搜答案-拍题作业网

Xi1.11.93Yi5.010.414.6E(X)=(1.1+1.9+3)/3=2E(Y)=(5.0+10.4+14.6)/3=10E(XY)=(1.1×5.0+1.9×10.4+3×14.6)/3

和E（X）一样啊.E（X）=西格玛X/n,所以E（XY）=西格玛（X*Y）/n.事实上就这么算的.举例?X1=3,X2=4,X3=8,Y1=2,Y2=5,Y3=5E(XY)=(3*2+4*5+8*5)

(x³+y³)dx-3xy²dy=0,齐次方程的通解?dy/dx=(x³+y³)/3xy²=(1/3)[(x/y)²+(y/x)]

xy'=y+xy的

xdy=(y+xy)dxdy/y=((1+x)/x)dxln|y|=ln|x|+x+cy=±e^(ln|x|+x+c)其中c是常数再问：真还不理解我们是选择题：y=cxe^xy=c+x-x^2y=cs

该题为隐函数求导.xy+e^(xy)=1则y+xy'+e^(xy)(y+xy')=0解得：y'=-y/x解答完毕.

1、求值：4x的2次幂y-【6xy-2（4xy-2）-x的2次幂】+1,其中x=-2分之1=4x²y-(6xy-8xy+4-x²)+1=4x²y+2xy-4+x²

xy=e^(x+y)两边对x求导得：y+xy'=e^(x+y)(1+y')解得：y'=(e^(x+y)-y)/(x-e^(x+y))=(xy-y)/(x-xy)dy=[(xy-y)/(x-xy)]dx

[(3x的2次幂y+2xy的2次幂)除以xy]的2次幂=（3x+2y)²=9x²+12xy+4y²

其次指各项变量的幂次相同例子的幂次都是2

xy=e^x-e^yd(xy)=d(e^x-e^y)xdy+ydx=e^xdx-e^ydy(x+e^y)dy=(e^x-y)dx则由dy/dx=(e^x-y)/(e^y+x)

令x=0,y=-1代入原式得值为1,选C

Cov(X,Y)=E(((X-E(X))(Y-E(Y)))根据协方差定义=E(xy-xE(y)-yE(x)+E(x)E(y))=E(xy)-E(x)E(y)-E(x)E(y)+E(x)E(y)=E(x

两边分别求x的导数得：e^x+(y+xy')=0,即y'=-(e^x+y)/x,即：dy/dx=-(e^x+y)/x

x²+xy=99x(x+y)=9*11x(x+y)=9*(9+2)x=9,y=2

E=EX+EY

两边求导得y'·e^y+(y+xy')/(xy)+e^(-x)=0

1.不能确定,X和Y有无数个答案.2.能求出来.原式=xy^2-(x^3)(y^6)+(x^2)(y^4)=-3+27+9=33(注：x^2表示X的平方)

一式子减去二式子乘以2的差得x²-2xy-3y²=0(x+y)(x-3y)=0x=-y或x=3y当x=-y时代入一式3y²-y²=8y=±2当x=3y时代入一式

答：xy=x-e^(xy)e^(xy)=x-xy=x(1-y)两边对x求导：(xy)'e^(xy)=1-y-xy'(y+xy')e^(xy)=1-y-xy'ye^(xy)+xy'e^(xy)+xy'=