Answer:
angle BEF = 100 degrees
Step-by-step explanation:
For a regular 9-sided polygon (nonagon),
each exterior angle = 360/9=40 degrees
each interior angle = 180-40 = 140 degrees.
Referring to diagram, in the trapezoid (trapezium) BCDE, the base angles are 180-140 = 40 degrees.
Therefore angle DEB = 40 degrees
that leaves BEF = 140-40 = 100 degrees
