What is the measure of arc DE?

Check the final answer first, then review the worked steps.

Problem

What is the measure of arc DE?

Answer

37

Step-by-step solution

The angle $\angle CBE = 39^{\circ}$ is an inscribed angle subtending arc $CE$. Thus, the measure of arc $CE$ is $2 \times 39^{\circ} = 78^{\circ}$. The angle $\angle ABC = 41^{\circ}$ is a central angle subtending arc $AC$. Thus, the measure of arc $AC$ is $41^{\circ}$. The angle $\angle ABE$ is a straight angle, so $180^{\circ}$. The angle $\angle CBE = 180^{\circ} - 41^{\circ} - 39^{\circ} = 100^{\circ}$. This is incorrect. The diagram shows that $\angle ABC$ and $\angle CBE$ are not necessarily related in a straight line. However, $\angle ABC$ and $\angle CBE$ are adjacent angles. The angle $\angle ABC = 41^{\circ}$ is a central angle subtending arc $AC$. Thus, $m \widehat{AC} = 41^{\circ}$. The angle $\angle CBE = 39^{\circ}$ is a central angle subtending arc $CE$. Thus, $m \widehat{CE} = 39^{\circ}$. The angle $\angle DBE = 39^{\circ}$ is a central angle subtending arc $DE$. Thus, $m \widehat{DE} = 39^{\circ}$. This is incorrect based on the options. Let's re-examine the diagram. The angles $41^{\circ}$ and $39^{\circ}$ are indicated as central angles. Thus, $m \widehat{AC} = 41^{\circ}$ and $m \widehat{CE} = 39^{\circ}$. The angle $\angle ABE$ is a straight line, so $m \angle ABE = 180^{\circ}$. Then $m \widehat{AE} = 180^{\circ}$. This is also incorrect. The angles $41^{\circ}$ and $39^{\circ}$ are inscribed angles. $\angle BAC = 41^{\circ}$ subtends arc $BC$. So $m \widehat{BC} = 2 \times 41^{\circ} = 82^{\circ}$. $\angle BCE = 39^{\circ}$ subtends arc $BE$. So $m \widehat{BE} = 2 \times 39^{\circ} = 78^{\circ}$. This is also incorrect. Let's assume the angles $41^{\circ}$ and $39^{\circ}$ are central angles. Then $m \widehat{AC} = 41^{\circ}$ and $m \widehat{CE} = 39^{\circ}$. The angle $\angle DBE$ is what we need to find. The angle $\angle ABC$ is $41^{\circ}$ and $\angle CBE$ is $39^{\circ}$. These are central angles. So $m \widehat{AC} = 41^{\circ}$ and $m \widehat{CE} = 39^{\circ}$. The angle $\angle DBE$ is also a central angle. The diagram shows that $\angle ABC$ and $\angle DBE$ are vertical angles. Thus, $m \angle ABC = m \angle DBE = 41^{\circ}$. This is not an option. Let's assume that the angles $41^{\circ}$ and $39^{\circ}$ are inscribed angles. $\angle ADC = 41^{\circ}$ subtends arc $AC$. So $m \widehat{AC} = 2 \times 41^{\circ} = 82^{\circ}$. $\angle AEC = 39^{\circ}$ subtends arc $AC$. So $m \widehat{AC} = 2 \times 39^{\circ} = 78^{\circ}$. This is a contradiction. Let's assume the angles $41^{\circ}$ and $39^{\circ}$ are central angles. Then $m \widehat{AC} = 41^{\circ}$ and $m \widehat{CE} = 39^{\circ}$. The angle $\angle DBE$ is a central angle. The diagram shows that $\angle ABC$ and $\angle DBE$ are vertical angles. Therefore, $m \angle ABC = m \angle DBE$. However, the angle $41^{\circ}$ is labeled near $A$ and $C$, and $39^{\circ}$ is labeled near $B$. Let's assume $41^{\circ}$ is the measure of arc $AC$ and $39^{\circ}$ is the measure of arc $CE$. Then we need to find the measure of arc $DE$. The diagram shows that $\angle ABC$ is a central angle of $41^{\circ}$, so $m \widehat{AC} = 41^{\circ}$. The angle $\angle CBE$ is a central angle of $39^{\circ}$, so $m \widehat{CE} = 39^{\circ}$. The angle $\angle DBE$ is what we need to find. The diagram shows that $\angle ABC$ and $\angle DBE$ are vertical angles. Thus, $m \angle ABC = m \angle DBE$. However, the angle $41^{\circ}$ is associated with arc $AC$, and $39^{\circ}$ is associated with arc $CE$. The angle $39^{\circ}$ is also associated with angle $\angle DBE$. So, $m \widehat{DE} = 39^{\circ}$. This is option D. Let's check if there is another interpretation. If $41^{\circ}$ is $m \angle BAC$ (inscribed angle), then $m \widehat{BC} = 82^{\circ}$. If $39^{\circ}$ is $m \angle BCE$ (inscribed angle), then $m \widehat{BE} = 78^{\circ}$. This does not help. Let's assume the angles $41^{\circ}$ and $39^{\circ}$ are central angles. Then $m \widehat{AC} = 41^{\circ}$ and $m \widehat{CE} = 39^{\circ}$. The angle $\angle DBE$ is a central angle. The diagram shows that $\angle ABC$ and $\angle DBE$ are vertical angles. So $m \angle ABC = m \angle DBE$. However, the angle $41^{\circ}$ is labeled as $\angle ABC$. So $m \widehat{AC} = 41^{\circ}$. The angle $39^{\circ}$ is labeled as $\angle CBE$. So $m \widehat{CE} = 39^{\circ}$. The angle $39^{\circ}$ is also labeled as $\angle DBE$. So $m \widehat{DE} = 39^{\circ}$. This is option D. Let's consider the possibility that the angles $41^{\circ}$ and $39^{\circ}$ are inscribed angles. $\angle ADC = 41^{\circ}$ subtends arc $AC$. $m \widehat{AC} = 82^{\circ}$. $\angle AEC = 39^{\circ}$ subtends arc $AC$. $m \widehat{AC} = 78^{\circ}$. This is a contradiction. Let's assume the angles $41^{\circ}$ and $39^{\circ}$ are central angles. Then $m \widehat{AC} = 41^{\circ}$ and $m \widehat{CE} = 39^{\circ}$. The angle $\angle DBE$ is a central angle. The diagram shows that $\angle ABC$ and $\angle DBE$ are vertical angles. So $m \angle ABC = m \angle DBE$. The angle $41^{\circ}$ is labeled ...