
I was surprised to see the R's cancel,
but of course they should. The central
angles are not related to the radius.
Now we
invoke the identies: and
.
Now sin 90º = 1, of course, and cos 90º =
0.
Now square both sides to get rid of the
radical.
We'll have to check our
results for extraneous solutions.
I looked at
this for a while. I expected the Pythagorean identity to help,
i.e. , hence
,
which factors thus:
, neither of
which cancels the denominator.
