(adsbygoogle = window.adsbygoogle || []).push({});

That's the image. I can't see how the edge of that middle triangle's length is Rθ at all. I've tried using similar triangles and law of cosines to figure that out but I'm missing lengths. I thought Rθ was the arc length of a piece of a circle? So if Rθ is a length of a piece of a circle, how is Rθ equal to that edge of the triangle?

**Physics Forums | Science Articles, Homework Help, Discussion**

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# How is this length R(Theta)? I don't see it...

**Physics Forums | Science Articles, Homework Help, Discussion**