[(x-4)/(x^2-1)]÷[(x^2-3x-4)/(x^2+2x+1)]+1/(x-1)=[(x-4)/(x-1)(x+1)]÷[(x+1)(x-4)/(x+1)^2]+1/(x-1)=[(x-4)/(x-1)(x+1)]*[(x+1)^2/(x+1)(x-4)]+1/(x-1)=1/(x-1)+1/(x-1)=2/(x-1)