Answer:[tex]\begin{gathered} (12).\text{ }-x^2y^3 \\ (13).\text{ }2t^2-6t+2 \end{gathered}[/tex]
Explanation:
12.
[tex]\begin{gathered} 4x^2y^3-5x^2y^3=-x^2y^3 \\ \end{gathered}[/tex]
13.
[tex]\begin{gathered} (8t^2-3t+1)-(6t^2+3t-1) \\ =8t^2-6t^2-3t-3t+1+1 \\ =2t^2-6t+2 \end{gathered}[/tex]
