\[y(y - 5)(y + 5) - (y + 2)\left( y^{2} - 2y + 4 \right) =\]
\[= y\left( y^{2} - 25 \right) - \left( y^{3} + 8 \right) =\]
\[= y^{3} - 25y - y^{3} - 8 = - 25y - 8.\]