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briana.img

  • one year ago

Find the value of a .

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  1. briana.img
    • one year ago
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    I seriously just did a problem like this but I always forgot on how to use it

  2. misty1212
    • one year ago
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    HI!!

  3. misty1212
    • one year ago
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    looks like a law of cosines problem?

  4. anonymous
    • one year ago
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    sine law again.

  5. misty1212
    • one year ago
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    hmm i think you need cosines for this you do not know any angle opposite one of the known sides

  6. anonymous
    • one year ago
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    right you are. Cosine law required.

  7. briana.img
    • one year ago
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    \[\frac{ \sin52 }{ ? } = \frac{ sinb }{ 4 }\]

  8. misty1212
    • one year ago
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    \[a^2=b^2+c^2-2bc\cos(A)\] \[a^2=4^2+7^2-2\times 4\times \cos(52^\circ)\] and a calcullator

  9. misty1212
    • one year ago
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    hold the phone dear

  10. misty1212
    • one year ago
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    if you want to use the law of sines (which you do , because it is easiest) you need 3 out of the for numbers to make a ratio

  11. misty1212
    • one year ago
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    you do not have three out of any four, because you do not know the angle opposite any known side

  12. misty1212
    • one year ago
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    you can see you ran in to that problem when you wrote \[\frac{ \sin52 }{ ? } = \frac{ \sin(b) }{ 4 }\]

  13. misty1212
    • one year ago
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    you got only two of the four numbers, two are unknown so you must use the law of cosines for this one

  14. briana.img
    • one year ago
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    @misty1212 i got 5.52507014 from doing your way after square rooting

  15. misty1212
    • one year ago
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    i can check if you like, i didn't do it

  16. briana.img
    • one year ago
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    @misty1212 i think it's right but can you check it please

  17. misty1212
    • one year ago
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    http://www.wolframalpha.com/input/?i=sqrt%284%5E2%2B7%5E2-2*4*7*cos%2852%29%29

  18. misty1212
    • one year ago
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    5.52 rounded looks good

  19. briana.img
    • one year ago
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    @misty1212 could you help me with another problem? please

  20. misty1212
    • one year ago
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    or in your case 5.5 cause they rounded to one decimal place

  21. misty1212
    • one year ago
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    yeah but i can't read what they are trying to find the value of in this case you know two angles so you know all three and therefore you can use the law of sines

  22. misty1212
    • one year ago
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    what do they want, \(r\) ?

  23. briana.img
    • one year ago
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    @misty1212 trying to find the value of r which is reallyw eird

  24. misty1212
    • one year ago
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    ok what is the measure of the angle opposite \(r\)?

  25. briana.img
    • one year ago
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    @misty1212 there's no angle opposite of r that's the weird part

  26. misty1212
    • one year ago
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    of course there is lol

  27. misty1212
    • one year ago
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    it is labelled \(\huge R\)

  28. briana.img
    • one year ago
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    @misty1212 there isn't!!

  29. misty1212
    • one year ago
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    oh i see, you mean you don't know what it is

  30. misty1212
    • one year ago
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    lets find it total in the triangle is 180 so it is \[180-45-63=72\]

  31. briana.img
    • one year ago
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    @misty1212 oooh yeah lmao forgot you could do it like that

  32. misty1212
    • one year ago
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    now law of sines finishes it right?

  33. misty1212
    • one year ago
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    \[\frac{r}{\sin(72)}=\frac{22}{\sin(45)}\] etc

  34. briana.img
    • one year ago
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    @misty1212 so it's rearrange to 22sin72=rsin45?

  35. misty1212
    • one year ago
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    this time i notice they round to two places http://www.wolframalpha.com/input/?i=22sin%2872%29%2Fsin%2845%29

  36. misty1212
    • one year ago
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    that step is not necessary

  37. misty1212
    • one year ago
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    \[\frac{r}{\sin(72)}=\frac{22}{\sin(45)}\iff r=22\times\frac{ \sin(72)}{\sin(45)}\]

  38. misty1212
    • one year ago
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    i know some math teacher might have said "cross multiply" but they are silly \[\frac{x}{a}=\frac{b}{c}\iff x=\frac{ab}{c}\]

  39. briana.img
    • one year ago
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    @misty1212 r=29.58993453?

  40. misty1212
    • one year ago
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    yeah looks good

  41. briana.img
    • one year ago
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    @misty1212 thank you!!! you really helped me tonight htis lesson really got me messed up

  42. misty1212
    • one year ago
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    you're welcome!\[\huge \color\magenta\heartsuit\]

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