Question

a. a nonagon has diagonals.

Explanation:

Step1: Recall diagonal formula

The formula for the number of diagonals $d$ of an $n$-sided polygon is $d=\frac{n(n - 3)}{2}$.

Step2: Identify $n$ for non - agon

A non - agon has $n = 9$ sides.

Step3: Substitute $n$ into formula

Substitute $n=9$ into $d=\frac{n(n - 3)}{2}$, we get $d=\frac{9\times(9 - 3)}{2}=\frac{9\times6}{2}$.

Step4: Calculate result

$\frac{9\times6}{2}=\frac{54}{2}=27$.

Answer:

27