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Sum
factorise: 8 + 6(a + b) - 5(a + b)2
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Solution
8 + 6(a + b) - 5(a + b)2
Let a + b = x
(a + b)2 = x2
8 + 6 (a+b) - 5(a + b)2
= 8 + 6x - 5x2
= 8 + 10x - 4x - 5x2
= 2(4 + 5x) - x (4 + 5x)
= (4 + 5x)(2 - x)
= [4 + 5(a + b)] [2 - (a + b)]
(Substituting the value of x)
= [4 + 5a + 5b][2 - a - b]
Concept: Factorisation by Grouping
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