What is the angle of rotation

[nitzy0508]

Triangle ABC is rotated clockwise to create triangle A’B’C’. What is the angle of rotation?

 

[MarkFL]

What are your thoughts here?

 

[HallsofIvy]

Frankly it looks very basic to me. Is it the translation downward that is throwing you off? Also it helps to specific a center of rotation. Imagine rotating ABC 90 degrees clockwise about point A. What does it look like? (Actually draw it on a sheet of paper if that helps.) Where do B and C move to? What about 180 degrees? 270 degrees? Of course, rotating clockwise about A returns B and C to their initial positions.

 

[lev888]

Seems like there is no translation involved and the center of rotation should be determined.

 

[Paul Belino]

Take a snap shot of the picture on your cell phone. Now rotate your cell phone clockwise to get the same image A'B'C'. How much did you have to rotate your phone? Your phone may automatically flip it back and that's also a clue.