{{ item.displayTitle }}

No history yet!

Student

Teacher

{{ item.displayTitle }}

{{ item.subject.displayTitle }}

{{ searchError }}

{{ courseTrack.displayTitle }} {{ statistics.percent }}% Sign in to view progress

{{ printedBook.courseTrack.name }} {{ printedBook.name }} Vertical angles are formed by two intersecting lines, so we should look for intersecting lines on the diagram. One possibility, along with the corresponding vertical angle pairs, is highlighted on the diagram below.

It appears that $∠DFB$ is obtuse, but can this be guaranteed based on the information given on the diagram? Notice that the marker at $D$ indicates that $AE$ is perpendicular to $DC.$

This perpendicularity means that triangle $DFE$ is a right triangle, so it can be assumed that $∠DFE$ is acute. Since $∠DFE$ and $∠DFB$ are supplementary angles, this also means that $∠DFB$ is obtuse. Hence, $∠CFE$ and $∠DFB$ are two obtuse vertical angles.