Hello!
To find the side length you use the equation

a is side length
d is diagonal
Put in the number we know

Divide

Multiply
a = 19.091
The answer is 19.09
Hope this helps!
Answer:
All sides are the same length (congruent) and all interior angles are the same size (congruent). To find the measure of the angles, we know that the sum of all the angles is 1260 degrees (from above)... And there are nine angles... So, the measure of the angle of a regular nonagon is 140 degrees.
Step-by-step explanation: