#### Ashadowcalledregret

##### Member

- Joined
- Oct 17, 2020

- Messages
- 73

- Gender
- Female

- HSC
- 2020

Oke so, the hexagon had 10 equal sides and the perimeter was 80. So you first divide 80 by 10 and get 8.What did you guys get for the decagon question?

Each side was 8cm (or whatever units it was in), then a total rotation would equal 360°, so you divide that with 10. So that's 36°. So we now know that each triangle has the outer side as 8cm and the angle opposite to it as 36°.

Then you do 180 - 36. And divide that answer by 2. To find the 2 other angels. (Equal sides = Equal angles). Then you use the Sine rule for whichever, getting you sides a and b.

You proceed to use the COSINE rule to find the area. 1/2 × a × b × Cos(C).

And then you times your answer with 10 anddd that's your answer.