Given two adjacent angles $\angle \mathrm{DEA}$ and $\angle \mathrm{AEB}$ that together form a straight angle, what is the numerical sum of their degree measures?

• A. $180°$
• B. $90°$
• C. $270°$
• D. $360°$

Answer: (A)

Verified step by step guidance

1. Understand that two adjacent angles that form a straight angle lie next to each other and their non-common sides form a straight line.
2. Recall the definition of a straight angle: it measures exactly 180 degrees.
3. Since the two angles $\backslash (\backslash angle\backslash )\; DEA$ and $\backslash (\backslash angle\backslash )\; AEB$ are adjacent and form a straight angle, their measures add up to the measure of the straight angle.
4. Express this relationship mathematically as: \(\text{measure}(\angle DEA) + \text{measure}(\angle AEB) = 180^\circ\).
5. Therefore, the numerical sum of their degree measures is 180 degrees.