Solve Descriptive Geometry Homework - Pt. M to N Length (-50%)

[Equilibrium]

Homework Statement

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.

Homework 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.)

The Attempt at a Solution

This is a graphing subject... and I am 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 don't know where n lies... so this is my *problem*

and I am suspecting that n lies at the y coordinate... but can't still get the point n

I don't know if i posted this on the right thread but forgive me
please help and give some hints if there's any engineer/architect having knowledge of this...

 

[radou]

Are you using the Monge projection?

 

[Equilibrium]

Hi radou...
No I am 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 I am 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 can't 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 can't still get it...
plus the yellow point is the point m(4, 8 ,-2)

 

[radou]

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.