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答案:
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1.C. df(r, y)drf(xy)d.D. d
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2.2.设z=2f(xy),其中函数f可微则 A 2yf'(r, y)B.-2yf'(r,y)D
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3.设R是实数集合。在R上定义二元运算*如下x,y∈R,x*y=x y xy
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4.B. df(x. y)d.C. dy. f(ry)dxD. dyf(r, y)d.
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5.(xy -x)y" xy" yy'- 2y'=0, y= In xy
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6.C. D, @ A, M, Q, R, S, Y, X)
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7.∃x∀y(x y=2y)B.∀x∀y(xy=y)C.∀x∃y(xy=0)D.∀x(xy=x)
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8.已知D(X)=1,D(Y)=25,ρXY=0.4,则D(X-Y)=( )
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9.已知D(X)=1,D(Y)=25,ρXY=0.4,则D(X-Y)=()
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10.________1212 2x5,;y-y,“xy,xy" y“2(z-y),z-2(xy)'•x二X 'y,Ly二y,iz —0,xy二2xy,yz二zx—0