The ending tells you who is being addressed.
اُنْصُرْ — one man: no added ending.
اُنْصُرَا — two people: ا.
اُنْصُرُوا — men: وا.
اُنْصُرِي — one woman: ي.
اُنْصُرْنَ — women: pronominal نَ.
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Notice the Endings
The Imperative: Formation and Six Forms
The ending tells you who is being addressed.
اُنْصُرْ — one man: no added ending.
اُنْصُرَا — two people: ا.
اُنْصُرُوا — men: وا.
اُنْصُرِي — one woman: ي.
اُنْصُرْنَ — women: pronominal نَ.