we can do a triangle to solve the apothem
the upper angle is equal to 360 divided by 8 since 360 is a complete turn and an octagon is composed of 8 equal triangles, so is 45
now we take a triangle from the triangle to apply trigonometric ratios and solve a
the upper angle of the new triangle is the half of the original so is 45/2
now i will use the trigonometric ratio of tangent
![\tan (\alpha)=(O)/(A)](https://img.qammunity.org/2023/formulas/mathematics/college/6013fvijp27hj2d8kae4eeqs30iip3e1yu.png)
where alpha is the angle, O the opposite side drom the angle and a the adjacent side from the angle
so replacing
![\tan ((45)/(2))=(3.5)/(a)](https://img.qammunity.org/2023/formulas/mathematics/high-school/b3gv1v6wlfms8ewfmy1kg2g0iasrvps6s4.png)
and solve for a
![\begin{gathered} a=(3.5)/(\tan ((45)/(2))) \\ \\ a\approx8.4 \end{gathered}](https://img.qammunity.org/2023/formulas/mathematics/high-school/vjzewenl6qb3tzd8plys5ckk87b179vwet.png)
the aphotem is 8.4
and the formula of the area of the octagon is
![A=4* a* l](https://img.qammunity.org/2023/formulas/mathematics/high-school/riq20ldan0a0qahpvysi21hd5i7j9robn9.png)
where a is the aphotem and l the measure f each side so 7
replacing
![\begin{gathered} A=4*8.4*7 \\ A=235.2 \end{gathered}](https://img.qammunity.org/2023/formulas/mathematics/high-school/6zll8tg2xxfk9hcz19vhhg7e6u3ke23x0m.png)
the area is 235.2 square units