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anonymous

  • one year ago

Trig Sine and Cosine Law Am I correct? Please do not give answer but guide me. Thank you. Ok, I have a triangle with A= 60 degrees and two sides which are b = 12 and c = 17 Ok, this to me is a Side Angle Side problem SAS, which requires the Cosine Law. Ok to solve for \( a^2 \) we would use \( a^2 = b^2+c^2 -2\times b \times c \times cos A \) which would be \( a^2 = 12^2+17^2 -2\times 12 \times 17 \times cos 60 \) which will equal \( a = \sqrt{229}\) Ok, I have more to come but is that correct so far???

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  1. AbdullahM
    • one year ago
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    Splendid work so far!

  2. AbdullahM
    • one year ago
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    You are on the correct path :) Now we have to use Law of Sines to calculate the rest.

  3. anonymous
    • one year ago
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    Ok now when I use \( cos B = \frac{\sqrt{229}^2+17^2}{2\times \sqrt{229}^2 \times 17} \) I get an error on my calculator....

  4. anonymous
    • one year ago
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    Why can't I find B like the following

  5. anonymous
    • one year ago
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    Do we have to use Sine Law to find the rest. Why can't we use Cosine Law like the above?? My calculator errors out.

  6. AbdullahM
    • one year ago
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    Using the Sin Law would be more easier :)

  7. Loser66
    • one year ago
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    You apply cos b formula wrong

  8. anonymous
    • one year ago
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    But Cosine should work correct?but my two calculators give errors

  9. Loser66
    • one year ago
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    \(b^2 = a^2+c^2 -2ac cosb\\2ac cosb= a^2+c^2 -b^2\\cosb=\dfrac{a^2+c^2-b^2}{2ac}\)

  10. anonymous
    • one year ago
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    Ah crap Loser66 you are right lol I forgot the -b^2 Man I thought I was losing my mind. I was like it should work LOL

  11. anonymous
    • one year ago
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    Thanks to you all.

  12. anonymous
    • one year ago
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    Still getting an error. Grrrrr lol

  13. Loser66
    • one year ago
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    why? what do you hit on your calculator? , You need \(\angle b\) right?

  14. anonymous
    • one year ago
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    Going to try my Ti nspire cx Still getting error on my Casio fx 115

  15. Loser66
    • one year ago
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    My calculator said that b is \(\approx 41^0\)

  16. anonymous
    • one year ago
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    Crap, I see where I made my mistake. I need to slow down. I hite times instead of plus

  17. anonymous
    • one year ago
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    I got 43.37 degreess

  18. Loser66
    • one year ago
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    hihihi... now, do it together: a^2 +c^2 -b^2 = 299 +17^2 -12^2 =444 ok?

  19. AbdullahM
    • one year ago
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    I got 43.47 also

  20. Loser66
    • one year ago
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    now divided by (2*17*sqrt (299) , we get 0.7552112641 ok?

  21. anonymous
    • one year ago
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    Cool, thanks Loser66 and AbdullahM, Sending you both 5 owlbucks. Thanks for the help

  22. anonymous
    • one year ago
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    I got it from here.

  23. AbdullahM
    • one year ago
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    Anytime :))

  24. Loser66
    • one year ago
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    now hit "2nd + cos^-1" then type 0.7552112641 it gives us 40.97463023

  25. Loser66
    • one year ago
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    hihihi... that's what my calculator said.

  26. AbdullahM
    • one year ago
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    Just to make sure, we can plug it into a calculator.

  27. AbdullahM
    • one year ago
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    http://www.mathwarehouse.com/triangle-calculator/online.php?&sb=12&sc=17&aa=60#triangleAppData

  28. Loser66
    • one year ago
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    sorry for correcting you again \(a=\sqrt{299}= 17.29\) not 15.13.. as you stated

  29. AbdullahM
    • one year ago
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    Her number is \(\bf 229\) not 299.

  30. Loser66
    • one year ago
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    oh yeah. my bad. I was wrong.

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