**Ask a monkey a physics question thread**

[OngBonga]

We can now write out a sine equation for the angle a/2.
sin(a/2) = {opposite}/{hypoteneus}
sin(a/2) = (c/2)/R
sin(a/2) = c/(2R)
a/2 = arcsin(c/(2R))

a = 2arcsin(c/(2R))

Ok am I right in thinking that the arcsin is basically the inverse, or reciprocal, of sin?

Also...

So the arc length is
R*a = 2R*arcsin(c/(2R))

Where's pi? It's not c/2r because c here is chord, not circumference.