设z=arccot(x+y),则zy′等于:()
A: 1/[1+(x+y)]
B: -sec(x+y)/[1+(x+y)]
C: -1/[1+(x+y)]
D:
A: 1/[1+(x+y)]
B: -sec(x+y)/[1+(x+y)]
C: -1/[1+(x+y)]
D:
C
举一反三
- 设函数z=f(x,y)=xy/(x2+y2),则下列结论中不正确的是() A: f(1,y/x)=xy/(x+y) B: f(1,x/y)=xy/(x+y) C: f(1/x,1/y)=xy/(x+y) D: f(x+y,x-y)=xy/(x+y)
- 实验命令“ syms x y; z=2*exp(x*y)+log(x+y); zx=diff(z,'x')”的结果是【】. A: 2*exp(x*y)+log(x+y); B: 2* y*exp(x*y)+1/(x+y); C: 2*x*exp(x*y)+1/(x+y); D: 无结果.
- int x=1,y=2,z; z=(x!=y)? x+y : x;则z= ________ 。
- int x=1, y=2, z=0; z= x > y ? x+y : x; 则z= ( )
- 下列哪个语句在Python中是非法的? A: x = y = z = 1 B: x = (y = z + 1) C: x, y = y, x D: x += y x=x+y
内容
- 0
设D(X)=25,D(Y)=1,Cov(X,Y)=2,则D(X+Y)=()。
- 1
设全体域D是正整数集合,确定下列命题的真值: (1) "x$y (xy=y) ( ) (2) $x"y(x+y=y) ( ) (3) $x"y(x+y=x) ( ) (4) "x$y(y=2x) ( )
- 2
A.yf’’x(xy)+φ’x(x+y)+yφ’’(x+y) A: φ’(x+y)+yφ’’(x+y) B: yf’’(xy)+φ’(x+y) C: yf’’(xy)+φ’(x+y)+yφ’’(x+y) D: 设,其中f,φ二阶可导,则等于()。
- 3
函数$z=\arcsin\dfrac{1}{~\sqrt{x+y}~}$的定义域为( ) A: $\left\{(x,y)\left|~x+y\geq<br/>0\right.\right\}$; B: $\left\{(x,y)\left|~x+y\geq<br/>1~\text{或}~x+y\leq<br/>-1 \right.\right\}$; C: $\left\{(x,y)\left|~x+y\geq<br/>1\right.\right\}$; D: $\left\{(x,y)\left|~x+y\geq<br/>\dfrac{4}{~\pi^2~}\right.\right\}$.
- 4
设X,Y为随机变量,且D(X+Y)=7,D(X)=4,D(Y)=1,则Cov(X,Y)=