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Question
Using the identity (a + b)(a – b) = a2 – b2, find the following product
(1 + 3b)(3b – 1)
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Solution
(1 + 3b)(3b – 1)
(1 + 3b)(3b – 1) can be written as (3b + 1)(3b – 1)
Substituting a = 3b and b = 1
In (a + b)(a – b) = a2 – b2, we get
(3b + 1)(3b – 1) = (3b)2 – 12
= 32 × b2 – 12
(3b + 1)(3b – 1) = 9b2 – 12
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