A.2
B.6
C.4
D.3
[主观题](15)若正实数x,y满足2x+y+6=xy,则xy的最小值是 .
[试题]若|x+2|+y-3=0,则xy的值为( )。A. -8B. -6C. 5D. 6
[单选题]已知函数的全微分df(x,y)=(3x2+4xy-y2+1)dx+(2x2-2xy+3y2-1)dy,则f(x,y)等于( ).A.B.C.D.
[单选题]已知函数的全微分df(x,y)=(3x2+4xy-y2+1)dx+(2x2-2xy+3y2-1)dy,则f(x,y)等于( ).A.B.C.D.
[单选题]已知函数的全微分df(x,y)=(3x2+4xy-y2+1)dx+(2x2-2xy+3y2-1)dy,则f(x,y)等于( ).A.B.C.D.
[问答题]若D(X)=25,D(Y)=16,ρxy=0.4,则D(2X+Y-3)=().
[单选题]已知x-y=1,则x3-3xy-y3的值为( )。A.1B.2C.3D.5
[问答题]设X~N(1,22),Y=2X+1,则ρXY=-------------.
[问答题]设X~N(1,22),Y=2X+1,则ρXY=----------------.
[单选题]已知实数x、y满足x2+y2=1,则(1-xy)(1xy)()。A . ['['有最小值,也有最大值1B . 有最小值,也有最大值1C . 有最小值,但无最大值D . 有最大值1,但无最小值