How do you calculate angles of a polygon?

1 Answer
Jan 29, 2016

Given only the lengths of polygon's sides, calculation of angles is possible for triangles and regular N-sided polygons.
In other cases angles cannot be defined.

Explanation:

In case of triangle, given all three sides a, b and c, we can use Theorem of Sines to get to the angles alpha, beta and gamma = pi - alpha - beta:
a/sin(alpha) = b/sin(beta) = c/sin(gamma)

For two unknown angles alpha and beta we have two equations:
a/sin(alpha) = b/sin(beta)
a/sin(alpha) = c/sin(pi-alpha-beta)
Solving them will give angles.

For N-sided polygons the interior angles are easily determined by a formula
alpha = (N-2)/N*180^o