What shape is made out of two congruent triangles?
If you have 2 EQUILATERAL triangles, and you stack them on their
respective hypotenuses, the result: SQUARE.
If you have 2 ISOSCELES triangles, and you stack them on their
respective hypotenuses, the result: RECTANGLE.
If you have 2 OBTUSE triangles, and you stack them on their
respective hypotenuses, the result: PARALLELOGRAM.