Answer:
a² - 5a - 36
Explanation:
(a - 9)(a + 4)
each term in the second factor is multiplied by each term in the first factor, that is
a(a + 4) - 9(a + 4) ← distribute parenthesis
= a² + 4a - 9a - 36 ← collect like terms
= a² - 5a - 36
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