二边取对数得:
lny=1/2[ln(x+1)+ln(x+2)-ln(x+3)-ln(x+4)]
二边对x求导:
y'/y=1/2[1/(x+1)+1/(x+2)-1/(x+3)-1/(x+4)]
所以:y'=1/2*根号(（x+1)(x+2)/(x+3)(x+4))*[1/(x+1)+1/(x+2)-1/(x+3)-1/(x+4)]