2021年考研(数学一)真题
2021年考研(数学一)真题选择题---为题目类型1.函数f(x)= \cases { \frac {e^{x}-1}{x},&x \neq 0, \cr 1,&x=0}(A)连续且取极大值(B)连续且取极小值(C)可导且导数为0(D)可导且导数不为0 2.设函数f(x,y)可微,且f(x+1,e^{x})=x(x+1)^{2},f(x,x^{2})=2x^{2} \ln x, 则df(1,1)=()(A)dx+dy(B)dx-dy(C)dy(D)-dy 3.设函数, f(x)= \sin x/(1+x^{2})在x=0 处的3次泰勒多项式为ax+bx^{2}+cx^{3}, 则()(A)a=1,b=0,c=-7/6(B)a=-1,b=0,c=7/6(C)a=-1,b=-1,c=7/(D)a=-1,b=-1,c=7/6 4.设函数f(x)在区间[0,1]上连续,则\int _{0}^{1}f(x)dx=()A.\lim _{x \rightarrow 0} \sum _{k=1}^{2n}f(\frac {k}{2n})\frac {2}{n}(A)(B)(C)(D)5.二次型f(2,x_{3})=(x_{1}+x_{2})^{2}+(x_{2}+x_{3})^{2}-(x_{3}-x_{1})^{2} 的正惯性指数与负惯性指数依次为()(A)2,0(B)1,1(C)2,1(D)1,2 6.已知\alpha _{1}=[ \matrix {1 \cr 0 \cr 1}], \alpha _{2}=[ \matrix {1 \cr 2 \cr 1}], \alpha _{3}=[ \matrix {3 \cr 1 \cr 2}], C \beta _{1}= \alpha _{1}, \beta _{2}= \alpha _{2}-k \beta _{1}, \beta _{3}= \alpha _{3}-1_{1} \beta _{1}-1_{2} \beta z,若β1,β2, β3 两两正交_(则1 1.2 依次为()A.\frac {5}{2}, \frac {1}{2} B.- \frac {5}{2}, \frac {1}{2} C.\frac {5}{2},- \frac {1}{2} D.- \frac {5}{2},- \f