两边取对数xlny=ylnx两边对x求导lny+xy'/y=y/x+y'lnx两边乘以xyxylny+y'x^2=y^2+y'xylnx移项y'x^2-y'xylnx=y^2-xylny提取公因式y'（x^2-xylnx）=y^2-xylnyy'=(y^2-xylny)/(x^2-xylnx)用含有y的式子表达y的导数...