Упростите выражение: (y^2+6y)^2-y^2(6+5y)(6-5y)-y^2(12y-y^2).

\[\left( y^{2} + 6y \right)^{2} - y^{2}(6 + 5y)(6 - 5y) - y^{2}\left( 12y - y^{2} \right) =\]

\[= y^{4} + 12y^{3} + 36y^{2} - y^{2}\left( 36 - 25y^{2} \right) - 12y^{3} + y^{4} =\]

\[= 2y^{4} + 36y^{2} - 36y^{2} + 25y^{4} = 27y^{4}.\]