Question

highlight the property (or properties) that will help you determine the unknown value.
opposite angles are congruent.
each diagonal bisects a pair of opposite angles.
the diagonals are perpendicular.
vertex angles measure 90°.

in rhombus abcd, what is the measure of ∠dec?
$m\angle dec$

Explanation:

Step1: Identify rhombus diagonal property

A rhombus has perpendicular diagonals.

Step2: Relate property to ∠DEC

Diagonals intersect at E, so $\angle DEC$ is formed by perpendicular lines.

Step3: Determine angle measure

Perpendicular lines form a 90° angle.

Answer:

$m\angle DEC = 90^\circ$
The key property used is: The diagonals are perpendicular.