cos(xy)(xy)'-[y/(x+1)-y']/y^2=0
cos(xy)(y+xy')-[y/(x+1)-y']/y^2=0
y'[xcos(xy)+1/y^2]=1/y(x+1)-ycos(xy)
y'=[1/y(x+1)-ycos(xy)]/[xcos(xy)+1/y^2]