多项式除法，商式和余式
a=1+e^xx=ln(a-1)dx=da/(a-1)原式=∫da/[a²(a-1)]1/[a²(a-1)]=m/a+n/a²+k/(a-1)m=n=-1,k=1原式=-∫da/a-∫da/a²+∫da/(a-1)=-lna+1/a+ln(a-1)+C=-ln(1+e^x)+1/(1+e^x)+x+C
