## AcidRa1n Group Title Picture 2 years ago 2 years ago

1. AcidRa1n Group Title

2. AcidRa1n Group Title

Ok how does angle C equal 20 and PS is 5?

3. AcidRa1n Group Title

Unkle it's not that hard come on...

4. UnkleRhaukus Group Title

there are 360° in a complete revolution, angle C is 1 eighteenth of the wayround $\angle C=360°/18$

5. AcidRa1n Group Title

wait what so how its it 20 on there?

6. UnkleRhaukus Group Title

did you simplify $$\angle C =\frac{360°}{18}=\dots$$

7. AcidRa1n Group Title

ohhh

8. UnkleRhaukus Group Title

$36=2\times18$ $360=2 \times 18\times10$

9. AcidRa1n Group Title

How would you find the area?

10. UnkleRhaukus Group Title

well the shape can be see as 18 of those little right angled triangle joined together, find the area of one then multiply by 18

11. UnkleRhaukus Group Title

|dw:1338432746562:dw|

12. AcidRa1n Group Title

ok wait

13. AcidRa1n Group Title

I have a diferent problem on my notes.. Same shape but it says each side = 4

14. AcidRa1n Group Title

What is the area.

15. AcidRa1n Group Title

|dw:1338433164896:dw|

16. AcidRa1n Group Title

like that

17. UnkleRhaukus Group Title

you can find length CS = a using a trigonometric function of the angle 20°

18. AcidRa1n Group Title

Lets say the question only give you the length of one side is 4

19. AcidRa1n Group Title

How would you go about finding the area?

20. UnkleRhaukus Group Title

|dw:1338432905847:dw|

21. AcidRa1n Group Title

|dw:1338433361442:dw|

22. AcidRa1n Group Title

Thats all it gives you. Find the area. I know it has something to do with finding the apothem and finding the perimeter and using the TAN function.

23. AcidRa1n Group Title

Half of one side is 2.

24. UnkleRhaukus Group Title

$\tan(20°)=\frac{\text{opposite}}{\text{adjacent}}=\frac5a$ $a=\frac 5{\tan(20°)}\neq4$

25. UnkleRhaukus Group Title

or is the 4 coming from a different problem/

26. UnkleRhaukus Group Title

the diagram posed at the top of the page does not have any side- length equal to 4

27. AcidRa1n Group Title

4 from a different problem

28. UnkleRhaukus Group Title

OK, what is the new problem exactly/

29. AcidRa1n Group Title

What I drew that's all it gives me

30. AcidRa1n Group Title

A decagon with a side lengths of 4. Find the Area.

31. UnkleRhaukus Group Title

well the first one was a nonagon so the picture is wrong

32. AcidRa1n Group Title

RAWRRRRRRRRR I HATE MATH SO MUCH OMFG

33. UnkleRhaukus Group Title

|dw:1338433609250:dw|

34. AcidRa1n Group Title

I DONT HAVE TIME FOR THISSSS I WANNA SLEEP

35. AcidRa1n Group Title

Yes now find the area. Just with that information.

36. UnkleRhaukus Group Title

well should i sing you a lullaby instead ?

37. AcidRa1n Group Title

LOL

38. UnkleRhaukus Group Title

ok so you might want to find the angle in triangle first, remember there are 360° in a revolution and i count 10 angles, so the angle in is $360°/10$

39. UnkleRhaukus Group Title

next find the length of the perpendicular , using the angle you just found and the tangent function

40. UnkleRhaukus Group Title

|dw:1338433908040:dw|, find the area of the triangle and lastly multiply this area by the number of those triangles in the decagon

41. AcidRa1n Group Title

360/10 =36? When I apply the TAN to 36 it's weird...

42. AcidRa1n Group Title

@UnkleRhaukus

43. UnkleRhaukus Group Title

true, what did you determine as an approximation of length b

44. UnkleRhaukus Group Title

2 significant figures is probably fine

45. AcidRa1n Group Title

huh? I didnt get that far becuase I thought you need to know the TAN of 36

46. AcidRa1n Group Title

@satellite73

47. UnkleRhaukus Group Title

yeah $\tan(36°)\approx0.727$

48. AcidRa1n Group Title

ok.. Let me see

49. UnkleRhaukus Group Title

$\tan(36°)=\frac{\text{opp}}{\text{adj}}=\frac 2 b$ $b=\frac {2}{\tan36°}\approx\cdots$

50. AcidRa1n Group Title

why is it b= 2/tan36?

51. AcidRa1n Group Title

Ohh I got it

52. AcidRa1n Group Title

so its 2.75

53. UnkleRhaukus Group Title

we are trying to find $$b$$ so we can work out the are of the triangle $\tan(36°)=\frac{\text{opp}}{\text{adj}}=\frac 2 b$ multiply both sides by $$b$$ then divide both sides by $$\tan36°$$

54. UnkleRhaukus Group Title

yes $$b\approx 2.75$$

55. AcidRa1n Group Title

so then after we find the area which is 2.752 we take the perimeter which is 40, and do 1/2* 2.752* 40

56. UnkleRhaukus Group Title

find the area of this triangle |dw:1338435087210:dw|

57. UnkleRhaukus Group Title

$A_{\triangle}=\frac{ab}2=\frac {2b}2=\cdots$

58. UnkleRhaukus Group Title

you dont need the perimeter

59. AcidRa1n Group Title

My notes has it O.o

60. AcidRa1n Group Title

Maybe hes teaching it like that?

61. AcidRa1n Group Title

THe formula for Area is. 1/2 * Apothem * perimeter

62. UnkleRhaukus Group Title

whatever, my method is better ~ so the area of the small right angled triangle is 2.752 and there are 20 of these in the decagon the the total area is simply $$A_{decagon}=2.752\times20=\cdots$$

63. AcidRa1n Group Title

Yeah lol same thing I got.

64. AcidRa1n Group Title

Well, thanks for taking like 30 minutes of your time to help me lol.

65. AcidRa1n Group Title

I'm so dumb.