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anonymous

  • one year ago

In triangle ABC, a = 3, b = 5, and c = 7. Find the approximate value of angle A.

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  1. mathmate
    • one year ago
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    Hint: cosine rule!

  2. anonymous
    • one year ago
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    oh ok use the quadratic formula

  3. anonymous
    • one year ago
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    22° 38° 142° 158° these are the answer choices

  4. anonymous
    • one year ago
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    \[\frac{ -b+-\sqrt{(b)-4(a)(c)} }{ ?2(a) }\]

  5. anonymous
    • one year ago
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    plug it in

  6. anonymous
    • one year ago
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    ok one second

  7. anonymous
    • one year ago
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    im still not understanding

  8. mathmate
    • one year ago
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    In geometry, it always helps to draw a diagram according to the given information. |dw:1434459130639:dw|

  9. mathmate
    • one year ago
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    cosine rule says: \(a^2=b^2+c^2-2(b)(c) cos(A)\) from which you can solve for cos(A): \(\Large cos(A)=\frac{b^2+c^2-a^2}{2bc}\) So you can substitute a,b,c into the equation and solve for angle A.

  10. anonymous
    • one year ago
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    and what do you get when you that because i keepp getting something different

  11. anonymous
    • one year ago
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    @kyrabaaker

  12. mathmate
    • one year ago
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    @jcwilliams504 What have you done so far?

  13. anonymous
    • one year ago
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    i plugged in everything but i dont know how to solve

  14. mathmate
    • one year ago
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    Do you know the values of a, b, and c?

  15. anonymous
    • one year ago
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    3,5, and 7

  16. mathmate
    • one year ago
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    Good, so what did you get for: \(\Large \frac{b^2+c^2-a^2}{2bc}\)

  17. anonymous
    • one year ago
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    65/70 :/

  18. anonymous
    • one year ago
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    @mathmate

  19. mathmate
    • one year ago
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    That's correct. You can find the angle A by solving cos(A)=65/70=13/14 or A = cos\(^{-1}\)(13/14)

  20. anonymous
    • one year ago
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    whats after that?

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