1) Considering that the formula for the number of diagonals of a polygon is:
[tex]D=\frac{n(n-3)}{2}[/tex]2) And the question tells us that we need to find the number of diagonals for a polygon that has 6 sides, we can plug into that n=6 and solve it this way:
[tex]\begin{gathered} D=\frac{6(6-3)}{2} \\ D=\frac{6\left(3\right)}{2}=\frac{18}{2} \\ D=9 \end{gathered}[/tex]