Geometry (angles)

[Sunset658]

I know the answer is 180 degrees but I'm having trouble explaining it.

 

[Sunset658]

Geometry and angles

I know the it 180 degrees but how do I explain it.

 

[mmm4444bot]

I don't like reading sideways; can you rotate your image, please?

I also cannot understand the pencil scribbles, on the diagram.

What have you tried or thought about, so far? Please explain where you got stuck.

Also, be sure to read the forum guidelines. Thanks! :cool: