Answer
$y^4-4y^2-4$
Work Step by Step
Removing the grouping symbols and then combining like terms, the given expression, $
[-(y^4-y^2+1)-(y^4+2y^2+1)]+(3y^4-3y^2-2)
,$ simplifies to
\begin{array}{l}\require{cancel}
[-y^4+y^2-1-y^4-2y^2-1]+3y^4-3y^2-2
\\\\=
-y^4+y^2-1-y^4-2y^2-1+3y^4-3y^2-2
\\\\=
(-y^4+3y^4-y^4)+(y^2-2y^2-3y^2)+(-1-1-2)
\\\\=
y^4-4y^2-4
.\end{array}
