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Question
Factorise the following:
(x + 3)(x – 3) – 40
Sum
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Solution
The given expression is,
(x + 3)(x – 3) – 40
= x2 – 9 – 40
= x2 – 49
Here we use the identity
a2 – b2 = (a + b)(a – b)
Taking a = x and b = 7, we get
∴ (x + 3)(x – 3) – 40
= x2 – 72
= (x + 7)(x – 7)
Thus, the fully factorised form is (x + 7)(x – 7)
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