Determine length of side of right triangle for given angle?

Discussion in 'Math' started by spinnaker, Oct 29, 2012.

  1. spinnaker

    Thread Starter AAC Fanatic!

    Oct 29, 2009
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    I have a solar panel mounted on a fence post. I need to adjust the panel angle throughout the year.

    Instead of requiring a protractor, I would like to make a graduated scale marked with the months. To make the job easier, I would like to measure one of the sides of the triangle to set the required angle.

    Example below. How would I calculate the length of side B for 26°?

    [​IMG]
    [​IMG]
     
  2. MrChips

    Moderator

    Oct 2, 2009
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    I believe, in this application A will be changing.
    You want to use the fixed length C.
    sin(angle) = B/C
    where the angle is in radians, i.e.

    angle in radians = (angle in degrees) x 3.14159 / 180
     
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  3. MrChips

    Moderator

    Oct 2, 2009
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    The correct equation is

    B = A * tan(angle)
     
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  4. Wendy

    Moderator

    Mar 24, 2008
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    Are you familiar with the law of sines? It is one of those formula I hang on to, because it tends to fill in for so many problems.

    A / Sine Angle A = B / Sine Angle B = C / Sine Angle C

    The Angles are opposite the sides. I'll stick in an illustration when I have more time.
     
    Last edited: Oct 29, 2012
  5. blah2222

    Well-Known Member

    May 3, 2010
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    This is correct, something seems to be in my water. Sorry about that.
     
  6. spinnaker

    Thread Starter AAC Fanatic!

    Oct 29, 2009
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    I take back my thanks. :)
     
  7. imasoundhound

    New Member

    Oct 28, 2012
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    you can't.

    you have to have the measure of at least one side of the triangle in order to use any of the trigonometric functions.

    assuming side C is the solar panel, and therefore of constant length, any change made to the angle formed by sides A and C will change the lengths of sides A and B (remember C doesn't change). If the measure of the angle increases, B must get longer while A gets shorter. If the measure of the angle decreases, B will get shorter while A gets longer.

    if C is of constant length, then:

    C*sin (26 degrees) = B

    and

    C*cos (26 degrees) = A
     
    Last edited: Oct 30, 2012
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