Answer
$t^9+5t^7$
Work Step by Step
By combining like terms, the given expression, $
(t^9+3t^6-8t^2)+(5t^7-3t^6+8t^2)
$, simplifies to
\begin{array}{l}\require{cancel}
t^9+3t^6-8t^2+5t^7-3t^6+8t^2
\\\\=
t^9+5t^7+(3t^6-3t^6)+(-8t^2+8t^2)
\\\\=
t^9+5t^7+0t^6+0t^2
\\\\=
t^9+5t^7
.\end{array}
