The Interactive Geometry Software Cinderella

Forum: Cinderella Support (E)

Forums->Cinderella Support (E)->basic arithmetic

SimonAbbott
1 stars
basic arithmetic


Thank you for writing this wonderful program!

I am using the free version of Cinderella 2. I was wondering if there was any way of performing basic arithmetical calculations on lengths and angles measured in a construction. Specifically, I am looking for a way to display the cross-ratio (BC:CD):(BE:ED) of four points BCDE on a line (see attached construction).


Simon

attachment Cross-ratio.cdy (5.21 Kb)
 
on: Fri 17 of Jun, 2011 [14:38 UTC] reads: 129521

Posted messages

author message
Aw: basic arithmetic
on: Fri 17 of Jun, 2011 [22:22 UTC]
Simon,

yes, you can do that. Just press the f(x) button (you might have to enable the complete toolbar in the configuration menu) to add the formula

(|B,C|/|C,D|)/(|B,E|/|E,D|)

You can also create the distances |B,C| by dragging from B to C while entering the formula.

I attach the construction.

Hope that helps
Ulli

PS: In your construction you move the crossing line by moving B and C — this makes it difficult to demonstrate the invariance of the cross ratio. I suggest you add two more points that are used for positioning the line and create "lines through point A" that won't move. I changed that for my example...


attachment Cross-ratio-new.cdy (4.27 Kb)

author message
SimonAbbott
1 stars
Re: Aw: basic arithmetic
on: Sat 18 of Jun, 2011 [14:22 UTC]
Very helpful. Thank you!


Simon



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