Answer:
![A=906.9\ cm^2](https://img.qammunity.org/2021/formulas/mathematics/college/mmb6hm9c73496357ollkajtprj9ed366i4.png)
Explanation:
A do-decagon is a polygon with 12 straight sides and 12 equal angles.
-The general formula for finding area of a do-decagon is given as:
![A=3(2+√(3))s^2](https://img.qammunity.org/2021/formulas/mathematics/college/5v3os0rlijh6i8ib6grzjaszgs0cl6msk1.png)
where s is the sides length.
-Given the sides dimension is 9cm, the area is calculated as;
![A=3(2+√(3))s^2\\\\=3(2+√(3))* 9^2\\\\=906.8883462\approx906.9\ cm^2](https://img.qammunity.org/2021/formulas/mathematics/college/h5vcks2owyltdalslfql20emt06b6uh82p.png)
Hence, the do-decagon's area is
![906.9\ cm^2](https://img.qammunity.org/2021/formulas/mathematics/college/w0kvkd7n3odl70ebn5884hvhz2pr2u74ey.png)