 Suppose the small square has area one square unit:
 The two small congruent triangles make a square congruent to the one above, which has area one square unit:
 Since the small square has area one square unit, each of the triangles must have area onehalf square unit:
 This is a parallelogram:
 Each of the triangles has area onehalf square unit, so the parallelogram must have area one square unit:
 This is the mediumsize triangle:
 Each of the triangles has area onehalf square unit, so the mediumsize triangle must have area one square unit:
 This is a large triangle:
 Since the small square has area one square unit and each of small triangles has area onehalf square unit, the large triangle must have area two square units:
 Since each large triangle has area two square units, the large square must have area four square units:
