D(X)存在,Pxy
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D(x)+D(y)
4x^2-pxy+9y^2p=124x^2-pxy+9y^2=(2x-3y)^2x^2表示x的平方
C=4-3-39所以x的方差是4,Y的方差是9,COV(X,Y)=-3所以相关系数=COV(X,Y)/[根号(4*9)]=-3/6=-1/2
Pxy根号[D(X)D(Y)]=Cov(X,Y)0.4*30=Cov(X,Y)Cov(X,Y)=12D(X-Y)=D(X)+D(Y)=61
当x<0时,-x>0,∴f(-x)=|-x-a|-a=|x+a|-a∴f(x)=-f(-x)=a-|x+a|f(x)定义域为R,x∈R,则x+2∈R,成立f(x+2)>f(x)当x≤-2时,a-|x+
D(x-y)=D(X)+D(Y)-2cov(x,y)cov(x,y)=pxy*√(D(X)*D(Y))=0.5*√4*1=1代入:D(2x-3y)=4D(X)+9D(Y)-2*2*3cov(x,y)=
Pxy是相关系数?应该是等于零
因为X~B(10,0.5),N(2,10),所以EX=10×0.5=5,DX=10×0.5×0.5=2.5,EY=2,DY=10,又E(XY)=14,所以X与Y的协方差为cov(X,Y)=14-5×2
(1)y=f(x)d^2y/dx^2=d(f'(x))/dx=f''(x)(2)y=ln[f(x)]dy/dx=f'(x)/f(x)d^2y/dx^2=d[f'(x)/f(x)]/dx=[f''(x)
lg3^x=lg10=1x=1/lg3选A啦3
当x-t小于零的时候即x-tx的时候不等式化简x^2t因为x
|p+2|>=0q-8q+16=(q-4)2>=0|p+2|与q-8q+16互为相反数所以p=-2q=4x²+y²+2xy-4=(x+y)2-4=(x+y-2)(x+y+2)
var(x+y)=var(x)+var(y)+0.4*5*6*2=85var(x-y)=25+36-24=37再问:为什么这么做呢?能写详细一点么,要交作业呢,求教了。比如什么公式之类的?
D(x+y)=Dx+Dy+2*cov(x,y)=Dx+Dy+2*Pxy*Dx(开方)*Dy(开方)=4+9+2*0.4*2*3=17.8D(x-y)=Dx+Dy-2*cov(x,y)=Dx+Dy+2*
解√p-2与q^2-8q+16互为相反数∴√p-2+(q^2-8q+16)=0∴√p-2+(q-4)^2=0∴p-2=0,q-4=0∴p=2,q=4∴x^2+y^2-(pxy+q)=x^2+y^2-(
p+2的绝对值与q平方-8q+16互为相反数即p+2的绝对值+q平方-8q+16=0所以p+2=0,(q-4)²=0p=-2,q=4x^2*y^2-(2pxy-q)=x²y
|P+2|>=0q²-8q+16=(q-4)^2>=0|P+2|与q²-8q+16互为相反数则P+2=0P=-2(q-4)^2=0q=4(X²+y²)-(pxy
-0.2*2*3=-1.2