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Question
Use suitable identity to find the following product:
(3x + 4) (3x – 5)
Solution
Given, (3x + 4) (3x – 5)
Hence, using a suitable identity,
(3x + 4) (3x – 5)
= (3x + 4) [3x + (–5)]
Using the identity (x + a) (x + b) = x2 + (a + b)x + ab, we get that,
(3x)2 + [4 + (–5)]3x + [4 × (–5)]
= 9x2 + (4 – 5)3x + (–20)
= 9x2 + (–1)3x – 20
= 9x2 – 3x – 20
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