浙江科技学院2020年数学分析
解
1、
$\displaystyle \lim_{x\to 0}\frac{\sin2x+xf(x)}{x^3}=\lim_{x\to 0}\frac{2x+o(x)+xf(x)}{x^3}=\lim_{x\to 0}\frac{2+f(x)}{x^2}=0.$
2、 $\displaystyle f(x)=a\sin x+\frac{1}{3}\sin 3x,$
$\displaystyle f'(x)=a\cos x+\cos 3x=0,$
$\displaystyle a=\frac{-\cos 3x}{\cos x}|_{t=\frac{\pi}{3}}=2.$
3、
$\begin{align*}I&=\int_{0}^{1}dy\int_{\arcsin y}^{\frac{\pi}{2}}f(x,y)dx+\int_{1}^{0}dy\int_{\frac{\pi}{2}}^{\arcsin y}f(x,y)dx\\\\&+\int_{0}^{-1}dy\int_{\arcsin y}^{\frac{3\pi}{2}}f(x,y)dx+\int_{-1}^{0}dy\int_{\frac{3\pi}{2}}^{\arcsin y}f(x,y)dx.\end{align*}$