# Geometry (calculation)

Hello experts:

My geometry knowledge is a bit rusty... I need some assistance with a calculating a value.

Please see attached XLS which illustrates the shape (and includes the question).

EEH
Geometry-Calculation.xlsx
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Commented:
You can draw a line parallel to c that goes through the red point.
Once you do that, you will see that any point on the new line could be the red point.

You need more information.  Does the line from c to the red point go through the midpoint of c?
That would make it easy, because you would have another right triangle.
Commented:
If the red line is perpendicular to the centre of  c then you have enough information. Three pieces of information is enough to find anything on a triangle.
Commented:
I need to type faster:7)
AnalystAuthor Commented:
d-glitch:

When you refer to "mid point of c", I believe you're referring to the center of the red point, correct?   If so, the answer is 'yes'.

Thanks,
EEH
AnalystAuthor Commented:
Quick follow-up... no, the red point could be anywhere "inside" the triangle.   So, no, it is not always at the mid point of line c.

EEH
Billing EngineerCommented:
it depends on what is known about the angles between "c" and the red line and/or the green line within the angle "ac".
usually a "distance" between a line a point is a perpendicular to the line (and I take that as a premise)
then, the "design" for the green line seems to cut the angle "ac" in half.
as that angle can be determined, you have the length of the red line and the angle opposite to that, so the other 2 lengths can be determined.

Commented:
You do have a second right triangle.  The line from the red point to c, is perpendicular to c.  That is what distance means.

You need another piece of information.
The distance from the green point to the new right angle would be the easiest.
Either of the two new angles would work too.
AnalystAuthor Commented:
Guy Hengel [angelIII / a3]

The angle between c and red point is 90 degrees.

Since I don't know the distance from green point to red line (on c), how I can compute the distance of the green line (given that I know the length of the red line)?

EEH
Commented:
You can't, without specifying or measuring something else.

See my first post, and draw the line through the red point.
Any point on that line will satisfy the criteria you have set so far.

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Commented:
I also see that your drawing is not to scale, the 80 meter side seems to be much longer than the 100 meter side.
How accurate do you need to be.  A proper scale drawing might be all you need.

Commented:
One way I like to look at the question of whether or not you have enough information is to see if you can "slide" things around and not change any of the knowns.  The only constraints that I read for the red point are that it is inside the triangle and that it is a specified distance away from  the hypotenuse.  You can "slide" that point along the line segment inside the triangle and parallel to the hypotenuse (the black one in d-glitches illustration) and still meet these two conditions.  "Obviously" the distance from the green point to the red point will change.  That says that you don't have enough information to solve this.
AnalystAuthor Commented:
All - thank you for your comments.    Need to go back to the drawing board.   Again, I appreciate your assistance.

EEH
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