Question

factorise the following​

Answer 1

2a-b is the correct answer

Answer 2

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Here's your answer..

Answer :

We have –6a = (–3) × 2a and –3b = (–3) × b.

⇒ –6a – 3b = (–3) × 2a + (–3) × b = (–3)(2a + b)

Substituting this into the original expression, we get

(2a + b)2 – 6a – 3b – 4 = (2a + b)2 – 3(2a + b) – 4

For simplicity, let us assume 2a + b = x. So, our expression using this notation is x2 – 3x – 4.

For factorizing, an expression split the middle term in such a way that the product of the coefficients of the new terms is equal to the product of the coefficients of the first and last terms in the expression.

Here, product of co–effs of first and last terms = 1 × (–4) = –4

So, if the middle term –3x is split into two terms say ax, bx, then

a + b = –3 and ab = –4.

Observe that values –4 and 1 satisfy these equations.

⇒ x2 – 3x – 4 = x2 – 4x + x – 4

Observe that x is common for the first two terms and 1 is common for the next two terms.

⇒ x2 – 4x + x – 4 = x(x – 4) + 1(x – 4)

Now, (x – 4) is the common term.

∴ x2 – 3x – 4 = (x – 4)(x + 1)

Thus, the factors of x2 – 3x – 4 are (x – 4) and (x + 1).

However, we assumed x = 2a + b.

⇒ x – 4 = 2a + b – 4 and x + 1 = 2a + b + 1

Hence, the factors of (2a + b)2 – 6a – 3b – 4 are (2a + b – 4) and (2a + b + 1).

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