Упростите выражение (((y+1)/(y-1))/(3y+1)/(y^2+y).

\[\left( \frac{y + 1^{\backslash y + 1}}{y - 1} - \frac{y^{\backslash y - 1}}{y + 1} \right)\ :\frac{3y + 1}{y^{2} + y} =\]

\[= \frac{y^{2} + 2y + 1 - y^{2} + y}{(y - 1)(y + 1)} \cdot \frac{y(y + 1)}{3y + 1} =\]

\[= \frac{(3y + 1) \cdot y}{(y - 1)(3y + 1)} = \frac{y}{y - 1}.\]