(y-2)/(y^2-1) - (y-1)/(y^2+y)= (y-2)/(y-1)(y+1) - (y-1)/y(y+1)=
[(y(y+1)(y-2)-(y-1)(y-1)(y+1)]/y(y-1)(y+1)=(y+1)(y(y+1)-(y-1)^2)/(y(y+1)(y-1)=
= (y+1)(y^2-2y-y^2+2y-1)/y(y-1)(y+1)= (y+1)/y(y+1)(y-1)=1/y(y-1)
при у=3 получим 1/6
