(2)分离变量得ydy/(y^2-1)=xdx/(1+x^2),[1/(y+1)+1/(y-1)]dy=2xdx/(1+x^2),积分得ln(y^2-1)=ln(1+x^2)+lnc,所以y^2-1=c(1+x^2).y=土√[1+c(1+x^2)].(4)仿上，ye^ydy=e^(-x)dx,(y-1)e^y=-e^(-x)+c.(6)dy/y=2xdx,lny=x^2+lnc,y=ce^(x^2).
