# 1. Which angle is included between the sides $\overline{DE}$  and $\overline{EF}$ of  $\bigtriangleup DEF$?

Since both the sides  $\overline{DE}$  and $\overline{EF}$ intersects at E,
$\angle E$  is included between the sides $\overline{DE}$  and $\overline{EF}$ of  $\bigtriangleup DEF$.