Rule 1: The three madd letters and their conditions
A letter is a madd letter only when two conditions meet: it carries no vowel, and the letter before it carries the matching short vowel. Alif is always sākin and is always preceded by fatḥa. Wāw must be sākin and preceded by ḍamma. Yāʾ must be sākin and preceded by kasra. The word نُوحِيهَا (11:49) contains all three in order: ū after ḍamma, ī after kasra, ā after fatḥa. If wāw or yāʾ carries a vowel (وَلَا, يَوْمِ) or follows a different vowel (خَوْفٍ), it is not a madd letter.
مَالِكِ
māliki
Master
alif after fatḥa: ā for two counts (1:4).
أَعُوذُ
aʿūdhu
I seek refuge
wāw sākin after ḍamma: ū (113:1).
تَرْمِيهِم
tarmīhim
pelting them
yāʾ sākin after kasra: ī (105:4).
نُوحِيهَا
nūḥīhā
We reveal it
all three madd letters in one word (11:49).
اَلْكَافِرُونَ
al-kāfirūna
the disbelievers
ā in كَا and ū in رُو, each two counts when continuing (109:1).