## dessyk 3 years ago need help im going to draw a triangle and im doing the law of sines so if anyone can help please do cuz im confused.. please click this to helpp

1. dessyk

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2. GT

Do you need to find a?

3. dessyk

so let me explain im trying to find a okay c=96.3, b=145.67 , B=39.5degrees, C=74.2degrees,

4. dessyk

law of sines is a/sinA=b/sinB

5. GT

Sine rule says: SinA/a = SinB/b = SinC/c

6. dessyk

okay i understand that waitt why is it sina/a instead of a/sin a

7. GT

SinA/a = Sin(39.5)/145.67 SinA = a*something

8. GT

Because they mean the same thing. A/B = C/D => B/A = D/C

9. dessyk

waitt does it even matter

10. dessyk

okay im not understanding

11. GT

You can find angle A by simply subtracting angles B and C from 180.

12. dessyk

okay i understand which would be 66.8

13. GT

Then, use this: SinA/a = Sin(39.5)/145.67 SinA = a*something SinA/something = a To find a.

14. GT

SinA/a = SinB/b = SinC/c IS SAME AS a/SinA = b/SinB = c/SinC

15. dessyk

but then a would be .00436

16. GT

I am getting 210.5

17. GT

That "something" in my expression is 0.00436. Divide Sin66.8 by that "something" value. Then, you get the value of a.

18. dessyk

really then let me try again...... im still not getting that are you multiplying or dividing

19. GT

SinA/a = Sin(39.5)/145.67 SinA = a*0.00436 a = SinA/0.00436 a = Sin66.8/0.00436 a = 210.5

20. dessyk

im not getting it first you divided than you did something else im so confused

21. dessyk

ok

22. dessyk

23. GT

Post it separately.

24. dessyk

i dont understand

25. imagreencat

26. dessyk

okay, so instead of 66.8 its 66.3

27. dessyk

im so fustrated im confusedd

28. GT

Punch it into the calculator and you get slightly different number from 210.5

29. GT

SinA/a = Sin(39.5)/145.67 SinA = a*0.00436 a = SinA/0.00436 a = Sin66.3/0.00436 a = 210

30. dessyk

i neeed helpppp

31. dessyk

i got -47.99

32. imagreencat

Check your calculator first. I'm guessing you're getting different answers because your calculator is not in degree mode. That's why it's treating your angles differently.

33. dessyk

wait no i got -110.05

34. GT

How in the world can a length of a side of a triangle be negative? Can you show the arithmetic you used to get that number?

35. dessyk

yeppp m ycalculator wasnt in degree mode so let me try again

36. dessyk

yayy i got 209.69

37. GT

Good....close enough to 210. :)

38. dessyk

next problem b=58.2 c=68.3 C=51.3 degrees were gunna find a

39. GT

At this point, it is simply plugging in values into that sine rule ratios and cranking out numbers in a calculator. There is not much help you need.

40. dessyk

yeaa but i want to do it my self then have someone do it so i can nn check my answer to make sure its correct

41. dessyk

i got 7105. 88

42. dessyk

43. GT

It can't be that big.

44. GT

Angles are almost close to each other. So, side lengths have to be close to each other too.

45. dessyk

well i must be doing something wrong but sin68.3/51.3=.018111746

46. dessyk

128.7/.018111746=7105.88

47. GT

b=58.2 c=68.3 C=51.3 degrees SinB/b = SinC/c => SinB = 58.2 * Sin(51.3)/68.3 => SinB = 0.665 B = 41.68

48. dessyk

becuase i couldnt find A or B so i figured they were the same by suntracting 180-51.3

49. dessyk

ohhh ok so u must follow the formula

50. GT

Now that you know B, you find A by doing 180 - 51.3 - 41.68 = 87

51. dessyk

noww i get it

52. GT

SinA/a = SinC/c => a = c * SinA/SinC => a = 68.3 * Sin(87)/Sin(51.3) => a = 87.4

53. dessyk

ok

54. wombat

@dessyk The following variations of Law of Sines are the same: $\frac{a}{\sin(A)} = \frac{b}{\sin(B)}=\frac{c}{\sin(C)}$ and $\frac{\sin(A)}{a}=\frac{\sin(B)}{b}=\frac{\sin(C)}{c}$

55. GT

He got that. :)

56. wombat

ok :)

57. dessyk

hello

58. GT

yeah

59. dessyk

i have another question but hoew did you get 41. sometrhing but i got 45.42

60. GT

You mean for B = 41? I did the inverse sine function on the value 0.665.

61. dessyk

yes, ohh reallyy you see im confused now i thought u just i thought u just took .6650*68.3=45.42

62. GT

Sin(B) = 0.665 => B = inverse sine (0.665). On the calculator, you have to first press 0.665. Then, inv button, then the sin button.

63. GT

That gives you angle B.

64. dessyk

i didnt get that

65. jatinbansalhot

dessyk.. nice drawing.. :) :)

66. dessyk

thank you i guesss lol can yoiu help me!!

67. jatinbansalhot

what is the question

68. dessyk

its up above next problem b=58.2 c=68.3 C=51.3 degrees were gunna find a

69. dessyk

law of sines

70. jatinbansalhot

i didn't see above but u can find it very easily.. the formula is sin a / a = sin b / b = sin c / c or a /sin a = b / sin b = c / sin c use any of them what caters ur problem

71. dessyk

okay but when i tried i started to get fustrated because i wasnt getting the righ tanswer

72. jatinbansalhot

did my answer help u even a bit or not ?

73. dessyk

a little bit its just that i need help going through the process

74. petewe

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75. petewe

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76. petewe

get it?