The measure of each interior angle of a regular nonagon is
140o
We know that the sum of the interior angles of a polygon of n sides is equal to (- 2) 180o. Also, a nonagon has 9 sides.
Therefore,
9 Measure of each interior angle = (9 - 2) 180o
Measure of each interior angle of a nonagon = = 7 20o = 140o