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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} = x^{2}

8 + 6 (a+b) - 5(a + b)^{2}

= 8 + 6x - 5x^{2}

= 8 + 10x - 4x - 5x^{2}

= 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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