0
$\begingroup$

I'm trying to plot the lines $x=(y-5)/3=(z+3)/2, x=(y-7)/4=(z-10)/5$ on Geogebra but it doesn't seem to plot anything. What am I doing wrong here? I'm also using the form Line[point,direction vector], but Geogebra seems to take the direction vector as a point instead and it calculates a new direction vector $v=(1,-2,5).$ How can I fix this?

enter image description here

  • 0
    What are your exact inputs to GeoGebra? – 2017-02-16
  • 0
    On the picture it is Line[(0, 5, -3), (1, 3, 2)] (and for the second line: Line[(0, 7, 10), (1, 4, 5)]) – 2017-02-16
  • 1
    GeoGebra reads this a pair of points, not a point and a vector, and so uses the `Line[Point, Point]` form of the function. Wrap the second argument in `Vector[]` so that GeoGebra knows you meant that and not a second point. – 2017-02-16
  • 0
    Yes, the vector part was fixed by this, but still no line appears on the plot – 2017-02-16
  • 0
    `Line[(0,5,-3), Vector[(1,3,2)]]` and `Line[(0,7,10), Vector[(1,4,5)]]` work just fine for me. – 2017-02-16
  • 0
    Ok for some reason this worked for me also, but it was the same input...maybe because I edited it instead of retyping it..Anyhow, thanks a lot! – 2017-02-16
  • 0
    Could be. I’ve had edits behave unexpectedly from time to time. – 2017-02-16

1 Answers 1

0

Functions in GeoGebra are polymorphic, so you need to be careful to have the right types of arguments, especially when there are alternative forms of the function with the same number of arguments. In particular, there are two similar-looking forms of the Line function: Line[Point, Point] and Line[Point, Vector]. GeoGebra reads an ordered triple as a point, so the input Line[(0,5,-3), (1,3,2)] is interpreted as the former form of the function. In some situations, GeoGebra will silently coerce a point into a vector, but because of the ambiguity between these two forms of Line it doesn’t, so you have to turn the second argument into a vector explicitly: Line[(0,5,-3), Vector[(1,3,2)]].