"Το τετράγωνο και το ορθογώνιο είναι διαφορετικά σχήματα."

Translation: The square and the rectangle are different shapes.

[ErikdenB]

A square has four sides of the same length, and four 90 degree angles between them. A rectangle has the angles, but the sides don't necessarily need to be all of the same length. Thus, all squares are rectangles, but not all rectangles are squares, much like thumbs and fingers.
In case anyone was wondering :P

[johndelaroo]

A quadrangle is not usually a shape in English. It is a courtyard surrounded by buildings. It does not actually have to be four-sided, but usually is. The correct word is quadrilateral. A rectangle is a quadrilateral (a four-sided polygon) but a quadrilateral can also be some other four-sided shape such as a square or parallelogram. Thus, the quadrilateral and the rectangle are the same shapes in some circumstances.

[smarnv]

Quadrilateral is τετράπλευρο in Greek, though. See this image:

So… Το τετράγωνο είναι ένα ορθογώνιο. :)

[Sninguistics]

Ah, δεν είναι σωστό, όλα τα τετράγωνα είναι ορθογώνια! Μα όλα τα ορθογώνια δεν είναι τετράγωνα =)

[Nikos48739]

Oblong?

[LadyMac1000]

Yes I wrote that too

[Sigi_sk]

Is this mathematicaly correct?
I mean - if ορθο-γώνιο mean any shape with 4 right angles, then square is part of family ορθογώνιο.
Every square is right-angled (but not every right-angled is square).

[G.Georgopoulos]

Yes, but actually no. It's a sensible question but that's just how it is.

[Sigi_sk]

OK, now I see discussion above, older. I didn't see it in mobile, where I learn, I see it on the web only.

[Marva441926]

Does τετράγωνο mean "square" or does it mean "quadrangle", as a literal translation would suggest? The two are not the same.

[G.Georgopoulos]

Quadrangle=τετράπλευρο (=four-sided).

[adegreeoffreedom]

μερικές φορές >.>

[stephem61]

Το τετράγωνο είναι ενα ορθογώνιο!

[alan536138]

Or a square is a special case of a rectangle

[jaye16]

"διαφορετικά" means "different" it does not mean "special".

[alan536138]

The square is a special case of the rectangular shape

[jaye16]

See my comment above, in addition, the Greek sentence does not refer to..."rectangular shape" it simple says..."The square and the rectangle are different shapes."

Trying to interpret the sentence is not the same as translating. Duolingo makes translating easy just follow these tips

TIPS TO MAKE LEARNING EASIER and EFFECTIVE + HOW TO REPORT A PROBLEM
https://forum.duolingo.com/comment/22424028

And check out the Greek Forum here with more links.
https://forum.duolingo.com/topic/936