The Interactive Geometry Software Cinderella
Forums-> Cinderella Support (E)-> basic arithmetic-> Aw: basic arithmetic
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Aw: basic arithmetic
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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...
Cross-ratio-new.cdy (4.27 Kb)
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