Finding Angle at $\gamma$ - Help Requested

[Carla1985]

View attachment 6256
Hi,

could someone please tell me what theorem I need to be looking at to work out the angle at $\gamma$ please? I've worked out the rest but can't find a theorem for this one.

Thanks

 

[Euge]

Use the vertical angles theorem.

 

[Carla1985]

Use the vertical angles theorem.

Thanks but that just gives me the angle between the two straight lines. My impression was that $\gamma$ was the part of the angle up to the edge of the circle.

 

[Euge]

That would not make an angle, for an angle is formed by two straight lines. It would only make sense for $gamma$ to be the angle between those two lines.

 

[Carla1985]

That would not make an angle, for an angle is formed by two straight lines. It would only make sense for $gamma$ to be the angle between those two lines.

That would make things a whole lot easier. Thank you for your help!