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Question
Using the identity (x + a)(x + b) = x2 + x(a + b) + ab, find the following product
(6a + 9)(6a – 5)
Solution
(6a + 9)(6a – 5)
Substituting x = 6a, a = 9 and b = – 5
In (x + a)(x + b) = x2 + x(a + b) + ab, we get
(6a + 9)(6a – 5) = (6a)2 + 6a(9 + (– 5)) + (9 × (– 5))
62a2 + 6a(4) + (– 45)
= 36a2 + 24a – 45
(6a + 9)(6a – 5) = 36a2 + 24a – 45
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