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Question
factorise: a2 - 23a + 42
Sum
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Solution
a2 - 23a + 42 ...[42 = 21 × 2 and 21 + 2 = 23]
= a2 - 21a - 2a + 42
= a(a - 21) - 2(a - 21)
= (a - 21)(a - 2)
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Factorisation by Grouping
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