Orientation of angle between lines

Per Svensson shared this question 1 month ago


This has been bugging me for a while, and I tend to forget the solution from one time to another, so at least this will serve as a note to self.

Whenever I want to mark an angle between two lines, it never seems to appear where I intended. I've come to realise that the position appears to be dependent on the direction of the line. Here's an example:


The four lines are defined as going in different directions, hence the angles end up differently in each case. Limiting the blue angles to 0°–180° just flips them over to the green side.

Let"s say I want to mark all the straight angles inside the resulting rectangle, i.e. getting v13 and v42 to join v21 and v34. Is there a way of achieving this without superimposing four additional lines going in opposite directions?



Comments (2)


I guess there is always this method, but it feels cumbersome as well.


Any input appreciated,



I always use some extra points on the lines to define angles exactly where I want them displayed with Angle(Point, Point, Point) :) keeping in mind that ggb creates angles in counterclockwise direction. I haven't tried creating the unit vectors that define the direction of lines, but this looks a bit more cumbersome to me than just a couple of clicks to create extra points.

Just for reference: https://wiki.geogebra.org/e...

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