设y=e^cos^2*1/x,求dy
问题描述：
设y=e^cos^2*1/x,求dy
答
lny=cos^2(1/x)两边求导:1/ydy/dx=2cos(1/x)[cos(1/x)]'1/ydy/dx=2cos(1/x)[-sin(1/x)]*[-1/x^2]1/ydy/dx=2cos(1/x)sin(1/x)/x^21/ydy/dx=sin(2/x)/x^2dy=y[sin(2/x)]/x^2dxdy=[e^cos^2(1/x)]*[sin(2/x)]/x^2dx