Double (المثنى) in Arabic

Double (المثنى) in Arabic :

click the picture to enlarge

We can make Double / Mutsana (المثنى) by adding some letter to Single / Mufrod (مفرده):

1. Rafak, you can add alef and Nuun (ان) for example: ِرجلاَنِ , اثناَن
2. Nasab, you can add Yaa and Nuun (ين) for example: رجليْنِ , اثنيًنِ