设f(xy,x+y)=x2+y2+xy,则f'x(x,y)+f'y(x,y)=______. (A)2x+y (B)2y+1 (C)2y-1 (D)2x+1
设f(xy,x+y)=x2+y2+xy,则f'x(x,y)+f'y(x,y)=______.
(A)2x+y (B)2y+1 (C)2y-1 (D)2x+1
设f(xy,x+y)=x2+y2+xy,则f'x(x,y)+f'y(x,y)=______.
(A)2x+y (B)2y+1 (C)2y-1 (D)2x+1
已知y=ef(x),则y″=( ).
A.ef(x)B.ef(x)f″(x)
C.ef(x)[f'(x)+f″(x)] D.ef(x){[f'(x)]2+f″(x)}
设z=e2x(x+y2+2y),则点(1/2,-1)是该函数的______.
(A)驻点,但不是极值点 (B)驻点,且是极小值点
(C)驻点,且是极大值点 (D)偏导数不存在的点
设n阶矩阵A非奇异(n≥2),A*是A的伴随矩阵,则______.
(A)(A*)*=|A|n-1A (B)(A*)*=|A|n+1A
(C)(A*)*=|A|n-2A (D)(A*)*=|A|n+2A
设线性方程组Am×nX=b,则正确的是______.
(A)若AX=O只有零解,则AX=b有唯一解
(B)若AX=O有非零解,则AX=b有无穷多解
(C)若AX=b有两个不同的解,则AX=0有无穷多解
(D)AX=b有唯一解的充要条件是r(A)=n
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