For regular triliteral Form I past verbs, the common passive template is فُعِلَ: ḍamma on the first radical and kasra before the final radical.
ضَرَبَ → ضُرِبَ (struck → was struck)
كَتَبَ → كُتِبَ (wrote → was written)
فَتَحَ → فُتِحَ (opened → was opened)
This is a pedagogical extension for regular verbs, not additional quoted text from the book.
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Mafʿūl Mā Lam Yusamma Fāʿiluhu — The Passive Subject
For regular triliteral Form I past verbs, the common passive template is فُعِلَ: ḍamma on the first radical and kasra before the final radical.
ضَرَبَ → ضُرِبَ (struck → was struck)
كَتَبَ → كُتِبَ (wrote → was written)
فَتَحَ → فُتِحَ (opened → was opened)
This is a pedagogical extension for regular verbs, not additional quoted text from the book.