All vertex angles (also called "interior angles") of a regular
polygon have equal measures. If this regular polygon has n sides,
then the sum of all the interior angles is 150° times n. The sum
of the measures of all the interior angles of any polygon with n
sides is (n-2) times 180°. So we have this equation
Solve that and we get
So we have a 12-sided regular polygon (a regular dodecagon)
Now we'll connect all the vertices to the center,
There are 12 central angles all
with equal measure and since they
all add up to 360°, each one is
of 360° or 30°.
Edwin