Imagine a right triangle (formerly called a rectangled triangle). One side adjacent to the right angle is twice as long as the other. You will not find it very difficult to construct a square from 4 of these triangles.
But is it possible to construct a square from 5 of these triangles? And from 6? From 7?
These problems are derived from ‘doordenkertje’ 12 in the November 1969 issue of ‘Pythagoras’, a Dutch magazine in recreational mathematics. You will need some elementary geometry knowledge to solve this problem.
You can check your solution here
justpuzzles 
A ‘rectangled triangle’? I haven’t encountered that term before. I’m curious where you’ve seen it, just because it is interesting tracking down different ways to say things.
Here:
http://en.wikipedia.org/wiki/Triangle#By_internal_angles
Thank you. It’s a curious mention, though; I haven’t seen a source for this term.