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Factorization of Polynomials

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6/8/2020 Factorization of Polynomials

Factorisation of Quadratic Polynomials- Splitting the middle term

Factorisation of the polynomial ax 2


+ bx + c by splitting the middle term is as follows:

Step 1: We split the middle term by finding two numbers such that their sum is equal to the
coefficient of x and their product is equal to the product of the constant term and the
coefficient of x . 2

For example for the quadratic polynomial (x 2


+ 5x + 6) the middle term can be split as,
x + 2x + 3x + 6 
2

Here,2 + 3 = 5 and 2 × 3 = 6.

Step 2: Now, we factorise by pairing the terms and taking the common factors.
2
x + 2x + 3x + 6

= x(x + 2) + 3(x + 2)

= (x + 2)(x + 3)

Thus, x + 2 and x + 3 are factors of x 2


+ 5x + 6 .

Factorisation of Quadratic Polynomials - Factor theorem

 
To factorise a quadratic polynomial f (x) = ax + bx + c, find two numbers p and q such that
2

f (p) = f (q) = 0. Let us factorise the quadratic polynomial f (x) = x − 3x + 2.


2

(i) f (2) = 2 − 3(2) + 2 = 4 − 6 + 2 = 0


2

Hence, x − 2 is a factor of x − 3x + 2. 2

(ii) f (3) = 3 2
− 3 × 3 + 2 = 9 − 9 + 2 = 2 ≠ 0

Hence, x − 3 is not a factor of x 2


− 3x + 2 .

(iii) f (1) = 1 2
− 3 × 1 + 2 = 0

Hence, x − 1 is a factor of x − 3x + 2. 2

So, x − 1 and x − 2 are the factors of the quadratic polynomial x 2


− 3x + 2 .
2
x − 3x + 2 = (x − 2)(x − 1)

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