Question

look at this diagram: if $overleftrightarrow{df}$ and $overleftrightarrow{gi}$ are parallel lines and $mangle feh = 40^{circ}$, what is $mangle dec$?

Explanation:

Step1: Identify vertical - angle relationship

$\angle FEH$ and $\angle DEC$ are vertical angles.

Step2: Apply vertical - angle property

Vertical angles are congruent. So, $m\angle DEC=m\angle FEH$.

Answer:

$40$