1

I have a triangle ABC. I know how to draw and find the incentre O (Extensions → Render → Draw from triangle → Incentre).

I need to draw the three perpendiculars KO, LO, MO from the incentre O to sides of the triangle and then extend they outside of sides (blue lines on figure):

enter image description here

Question. Could you please give me an idea how to draw the three perpendiculars KO, LO, MO from the incentre O? Is there a build-in function or an extension?

Improve this question
2
  • 1
    … on-top your new question seems to be off-topic for this site as it is about implementing a mathematical algorithm in a programming language.
    – Wrzlprmft ♦
    Commented Sep 30, 2017 at 15:55
  • Maybe GeoGebra is an interesting tool for you?
    – user unknown
    Commented Oct 1, 2017 at 2:00

2 Answers 2

Reset to default
4

Here's one method. There may be others of course.

  1. Mark the origin of your incentre with guides.

  2. Draw squares from the intersection of each triangle side and guide, to the centre origin (hint: Hold down CTRL as you click and drag to constrain to a square).

  3. Rotate each square so that the other corner intersects with the triangle

  4. Draw a line from the centre origin, to the external corner of each square

  5. Delete the squares, and turn the perpendicular paths into guides using Object → Object to guides.

  6. Draw the perpendicular lines using the guides.

enter image description here

Improve this answer
3

The ckassical elementary construction of a normal from a given point by drawing three circles work. The orange line is the resulted normal:

enter image description here

It only needs trimming, See the next method for it.

If there's no need of a puristical glaze,

  • make copies of the triangle sides (=select, Ctrl+D). If the triangle happens to be a closed shape, it's no use to split it, but draw new lines with the pen tool. If you have the point snaps on and high zoom, they will fit perfectly.
  • rotate them 90 degrees (Object > Rotate 90 degrees)
  • move by dragging the line with the usual selection tool until the end snaps to the incentre
  • trim.

Trimming needs the node editing tool. Double click at the crossing to create a new node, delete the node from the exessive end. The extra part vanishes.

Be sure that all snaps to points are in use, no snap to the grid.

Here's a sparse non-live visualization of the costruction of one normal:

enter image description here

  1. one side is selected, duplicated and rotated 90 degrees

  2. dragged to the incentre

  3. trimmed

Improve this answer
2
  • thanks, how to split triangle into 3 sides? I can select the full object only.
    – Nick
    Commented Sep 30, 2017 at 7:42
  • @Nick I added something about it to the answer. But if you want to split, then take the node tool, select a corner point, click the "Break path" icon in the tool otions bar on the top of the screen.
    – user82991
    Commented Sep 30, 2017 at 8:48

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.