anonymous
  • anonymous
In triangle ABC, a = 3, b = 5, and c = 7. Find the approximate value of angle A.
Geometry
  • Stacey Warren - Expert brainly.com
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SOLVED
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chestercat
  • chestercat
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mathmate
  • mathmate
Hint: cosine rule!
anonymous
  • anonymous
oh ok use the quadratic formula
anonymous
  • anonymous
22° 38° 142° 158° these are the answer choices

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More answers

anonymous
  • anonymous
\[\frac{ -b+-\sqrt{(b)-4(a)(c)} }{ ?2(a) }\]
anonymous
  • anonymous
plug it in
anonymous
  • anonymous
ok one second
anonymous
  • anonymous
im still not understanding
mathmate
  • mathmate
In geometry, it always helps to draw a diagram according to the given information. |dw:1434459130639:dw|
mathmate
  • mathmate
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.
anonymous
  • anonymous
and what do you get when you that because i keepp getting something different
anonymous
  • anonymous
@kyrabaaker
mathmate
  • mathmate
@jcwilliams504 What have you done so far?
anonymous
  • anonymous
i plugged in everything but i dont know how to solve
mathmate
  • mathmate
Do you know the values of a, b, and c?
anonymous
  • anonymous
3,5, and 7
mathmate
  • mathmate
Good, so what did you get for: \(\Large \frac{b^2+c^2-a^2}{2bc}\)
anonymous
  • anonymous
65/70 :/
anonymous
  • anonymous
@mathmate
mathmate
  • mathmate
That's correct. You can find the angle A by solving cos(A)=65/70=13/14 or A = cos\(^{-1}\)(13/14)
anonymous
  • anonymous
whats after that?

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