12.设y=(x)/(1+x^2)，则dy|_(x=0)=_.

设函数y=(2+cos x)^x，则dy|_(x=0)=设函数$y=(2+\cos x)^{x}$，则$dy|_{x=0}=$

设y=dfrac(x{(1+x))^2}({(1-x))^3}，则y=A. $\dfrac{6+x-{x}^{2}}{x-{x}^{3}}$B. $\dfrac

方程 (x)/(1+y) dx - (y)/(1+x) dy = 0 满足 y|_(x=0) = 1 的特解为 _______。方程 $\frac{x}{1+y

12.求极限 lim _(xarrow 0)dfrac (sqrt {1+x+{x)^2}-1}(ln (1+x))

设 y = x arcsin x，则 dy = ( )。A. $(\arcsin x \cdot \frac{x}{\sqrt{1 - x^2}}) dx$B.

设 lim _(xarrow 0)dfrac (ln (1+x)-(ax+b{x)^2)}({x)^2}=2, 则设 lim _(xarrow 0)dfrac

设函数f（x）=(x)/(1+x^2)，则f（(1)/(x)）=（ ）A. -$\frac{x}{1-x^{2}}$B. $\frac{x}{1-x^{2}}$

12.设方程 +sqrt ({x)^2+(y)^2+(z)^2}=sqrt (2) 确定了函数 =z(x,y), 则z(x,y)-|||-在点 (1,0,-1)

y = x - (1)/(2) sin x，则 (dx)/(dy) = ____。A. $\frac{2}{2 - \cos y}$B. $\frac{2}{2

设区域 D=(x,y)|x^2+y^2 leq a^2, a >0, y geq 0，则 iint_(D)(x^2+y^2), dx , dy= _______