How can you make a concave hexagon from four triangles?

Answer 1

It's a bit hard to explain in words. Suppose you have four congruent isosceles triangles: ABC, DEF, GHI, and JKL. (the vertexes are A, D, G and J). Place DEF and ABC so that the bases are touching. You now have quadrilateral ABDC ( when 2 points coincide, use the letter which comes first in the alphabet).

Place GHI so that G is at B and H is at A. You now have quadrilateral AIDC (IBD is a straight line).

Place JKL so that L is at D and J is at B. Now AIBKDC is the concave hexagon.

Answer 2

I think you have to use four scalene