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Help With The Law of Sines

  1. May 23, 2016 #1

    MathWA

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    1. The problem statement, all variables and given/known data

    Find a by using The Law of Sines by knowing that c=12, angle A=42o, angle C=69o.
    2. Relevant equations
    (sin A)/a=(sin B)/b=(sin C)/c

    3. The attempt at a solution
    I tried putting it in, but all I got was this correct, but useless equation:
    6511/7990=383/470
    I did it 1 more time, but still it wasn't successful. :frown:
    Please Help!
     
  2. jcsd
  3. May 23, 2016 #2
    I am not sure how you go the numbers you did in the solution attempt. The sine of the angles will give you numbers less than 1. I get the answer 8.6 for a
     
  4. May 23, 2016 #3

    MathWA

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    Well, I did a lot of factoring with decimals, so I must had got them mixed up.
    By the way calculators are allowed.
     
  5. May 23, 2016 #4

    MathWA

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    The answer is actually 9.34, but I need the solution(step-by-step work).
     
  6. May 23, 2016 #5
    Show me your work.
     
  7. May 23, 2016 #6

    MathWA

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    I recalculated and got 61, instead, but its wrong!
     
  8. May 23, 2016 #7

    MathWA

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    Well, I got c equals to 50.
     
  9. May 23, 2016 #8
    Can you write out line by line what you are doing, please?
     
  10. May 23, 2016 #9

    MathWA

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    That would take a while, but sure, but not now(I'm very busy)
    I can give you the last couple of lines:
    (0.94)/a=47/ac
    c=50
    0.94/a=0.77/50
    47=0.77a
    a is about 61
     
  11. May 23, 2016 #10
    well, firstly if 0.94 is your answer to sin42, that isn't right. I get something closer in radian mode.
     
  12. May 23, 2016 #11

    MathWA

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    Oops, I typed the wrong problem!
    c is 12, angle A is 110, and angle C is 50
    Sorry about that rpthomps!
     
  13. May 23, 2016 #12
    So, is this work using the new values then? where did 47 come from?
     
  14. May 23, 2016 #13
    $$\frac{a}{sin110}=\frac{12}{sin50}$$

    This is how I would start it. THen I would use algebra to solve for the unknown.
     
  15. May 23, 2016 #14

    MathWA

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    I figured the problem out! Thank you, rpthomps!:smile::smile::smile:
     
  16. May 23, 2016 #15

    MathWA

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    I made the problem too confusing!
     
  17. May 23, 2016 #16

    Mark44

    Staff: Mentor

    Yes, this is useless. Since you're trying to solve for a, your equation here should have a in it somewhere.
    That's not how it works here. We'll help you get to a solution, but we aren't going to give it to you step by step.

    Start with what rpthomps write in post #13.
     
  18. May 23, 2016 #17
    You're welcome
     
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