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Homework Help: Descriptive geometry

  1. Dec 26, 2006 #1
    1. The problem statement, all variables and given/known data
    A line from point m(4,8,-2) is due south and has a grade of -50% to pt. n. complete the location of n(?,2,?) and give the true length of the line.

    2. Relevant equations
    Grade: \frac{rise}{run} x 100%
    The plane H, F and S - if someone knows about this other than me
    The bearing can only be determined in the horizontal plane (north south ETC.)

    3. The attempt at a solution
    This is a graphing subject... and im using an orthographic paper...
    Lemme explain....

    the point is m(4, 8, -2)... so the line downward is due south in the horizontal plane since the bearing can only be determined in the horizontal plane... but my *problem* is where is the line??

    The grade here is 50% so
    -50 / 100 = - 1 / 2
    so 1 to the rise and 2 to the run from n thus it is going down one unit and going to the left 2 units since it is negative... but i dont know where n lies... so this is my *problem*

    and im suspecting that n lies at the y coordinate... but cant still get the point n

    I dont know if i posted this on the right thread but forgive me
    please help and give some hints if theres any engineer/architect having knowledge of this...
    Last edited: Dec 26, 2006
  2. jcsd
  3. Dec 26, 2006 #2


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    Are you using the Monge projection?
  4. Dec 26, 2006 #3
    Hi radou...
    No im using the orthograpic projection w/c consists of three planes:
    in the Horizontal plane or H - lies x, and y axes
    Frontal plane or F - x, z
    Side plane or S - y , z

    See what i tried...
    im using autocad w/c is similar... but for real im really using the orthographic sheet... because this is a drafting subject
    see what I plotted
    so the lines from the H plane which i drew a line is due south in which i cant determine the line from south... and the other line is the line i marked which is 2 = y... in which it has the n coordinate i did this to make it easier but i cant still get it....
    plus the yellow point is the point m(4, 8 ,-2)
    Last edited: Dec 26, 2006
  5. Dec 26, 2006 #4


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    Hint (I hope it can be found useful): the line must intersect the plane which contains the point y = 2 and is perpendicular to the y-axis.
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