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Question
Using the identity (a + b)(a – b) = a2 – b2, find the following product
(4 – mn)(mn + 4)
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Solution
(4 – mn)(mn + 4)
(4 – mn)(mn + 4) can be written as (4 – mn) (4 + mn = (4 + mn)(4 – mn)
Substituting a = 4 and b = mn
In (a + b)(a – b) = a2 – b2, we get
(4 + mn)(4 – mn) = 42 – (mn)2
= 16 – m2 n2
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