lny=½[ln(x+4)-ln(x²-5)]
两端对x求导,得
y'/y=½[1/(x+4)-2x/(x²-5)]
y'=y×½[1/(x+4)-2x/(x²-5)]=½√[(x+4)/(x²-5)][1/(x+4)-2x/(x²-5)]