Correct Answer - Option 4 : 2x – 1
Given:
Polynomials are 6x3 + 19x2 + x – 6, 2x2 + 9x – 5, and 6x3 + 23x2 – 5x – 4
Concept used:
HCF of two polynomials ≤ Difference of the polynomials
Calculation:
As we know that HCF ≤ Difference of polynomial
⇒ HCF ≤ 6x3 + 23x2 – 5x – 4 – (6x3 + 19x2 + x – 6)
⇒ HCF ≤ 6x3 + 23x2 – 5x – 4 – 6x3 – 19x2 – x + 6
⇒ HCF ≤ 4x2 – 6x + 2
⇒ HCF ≤ 4x2 – 4x – 2x + 2
⇒ HCF ≤ 4x × (x – 1) – 2 × (x – 1)
⇒ HCF ≤ (4x – 2) × (x – 1) = 2 × (2x – 1) × (x – 1)
Now check weather (2x – 1) and (x – 1) are factor of 6x3 + 19x2 + x – 6 and 6x3 + 23x2 – 5x – 4 or not
We will check for 2x – 1 = 0
For x = 1/2, 6x3 + 19x2 + x – 6 = 0, and
For x = 1/2, 6x3 + 23x2 – 5x – 4 = 0
Now check for x – 1 = 0
For x = 1, 6x3 + 19x2 + x – 6 = 19 and,
For x = 1, 6x3 + 23x2 – 5x – 4 = 20
(2x – 1) is a factor of both 6x3 + 19x2 + x – 6 and 6x3 + 23x2 – 5x – 4
Now we have to check weather (2x – 1) is a factor of the third polynomial or not
For x = 1/2, 2x2 + 9x – 5 will be
⇒ 2 × (1/2)2 + 9 × (1/2) – 5
⇒ 1/2 + 9/2 – 5 = 0
⇒ 2x – 1 is a factor of 2x2 + 9x – 5
∴ HCF is 2x – 1