Translation:Algebra is different from geometry.
The usage of τη and την seems inconsistent. Here my answer of ... τη Γεωμετρία was marked wrong, but in another lesson, ... την Γεωμετρία was also marked wrong. Your reference material says that the ν is omitted before γ. Is there something I'm missing here? I've noticed similar discrepancies with το and τον.
Yes, the "ν" should be removed from this article. Thanks for bringing it to our attention. Your answer of "τη Γεωμετρία should have been accepted but not "*την Γεωμετρία". From what I see in the New Tree ti's all in order so we'll have to work on this tree to remove the incorrect use of "ν". Again thanks.
Ι'm also curious why duolingo insists on την before a γ. I realize it is common in some circles, but it isn't mandatory... or am I misunderstanding? I was taught that την (feminine "the" not pronoun "her") added the ν before vowels and the following consonantal sounds: π, κ, τ, μπ, γκ, ντ, ψ, ξ. Am I wrong (would not be the first time!).
You're right. We had both "τη" and "την" and I said (see the comment above yours) that I would remove "την". I don't know why it's still there but will look into it.
Ok, we've had a quick team discussion and will leave only "τη" as the main translation. We will accept 'την' for those who are still of the old school but it will never be introduced as the correct answer.