Rule 1: 1. The perfect of رَأَى
In رَأَى he saw the third radical is a weak letter, written as alif maqṣūra. Before the feminine ending ـَتْ it disappears altogether: رَأَتْ she saw keeps only the stem رَأَ; before the dual ending ـَا it is written as ي: رَأَيَا they two saw; before a consonant ending the weak letter appears as ـيْـ: رَأَيْتُ I saw. The only surprise is the masculine plural رَأَوْا they saw, where the weak letter is swallowed by the ending ـوْا. When a suffix follows, رَأَى is written رَآ: رَآهَا he saw her.
رَأَيْتُ ثَعْلَبًا فِي الْكَرْمِ.
raʾaytu thaʿlaban fi l-karmi
I saw a fox in the vineyard.
رَأَتِ الْعَنْزُ الْحُفْرَةَ وَلَمْ تَنْزِلْ.
raʾati l-ʿanzu l-ḥufrata wa-lam tanzil
The she-goat saw the pit and did not go down.
هَلْ رَأَيْتُمُ الْقَمَرَ أَمْسِ؟
hal raʾaytumu l-qamara amsi
Did you (pl.) see the moon yesterday?
رَأَوْا صَاحِبَ الْكَرْمِ فَهَرَبُوا.
raʾaw ṣāḥiba l-karmi fa-harabū
They saw the owner of the vineyard and fled.
رَأَوْا, not رَأَيُوا.
لَمَّا رَآهَا الثَّعْلَبُ ضَحِكَ.
lammā raʾāha th-thaʿlabu ḍaḥika
When the fox saw her he laughed.
رَأَى + هَا is written رَآهَا.