NCERT Exemplar Solutions
Class 10 - Mathematics - CHAPTER 2: Polynomials - Exercise 2.1
Question 6

Question.  6

If one of the zeroes of the cubic polynomial \(x^3+ax^2+bx+c\) is \(-1\), then the product of the other two zeroes is

(A)

\(b-a+1\)

(B)

\(b-a-1\)

(C)

\(a-b+1\)

(D)

\(a-b-1\)

Detailed Answer with Explanation:

Step 1: Use the fact that \(-1\) is a root.

Substitute \(x=-1\) in the polynomial:

\((-1)^3 + a(-1)^2 + b(-1) + c = 0\)

\(-1 + a - b + c = 0\)

So, \(c = b - a + 1\).

Step 2: Recall the relationship of roots with coefficients.

For a cubic polynomial \(x^3 + ax^2 + bx + c\), if the roots are \(\alpha, \beta, \gamma\), then:

\(\alpha + \beta + \gamma = -a\)

\(\alpha\beta + \beta\gamma + \gamma\alpha = b\)

\(\alpha\beta\gamma = -c\)

Step 3: Express product of the other two zeroes.

Let the roots be \(-1, r, s\).

Then \((-1)rs = -c\)

So, \(rs = c\).

Step 4: Substitute the value of \(c\).

Since \(c = b - a + 1\), we get

\(rs = b - a + 1\).

Final Answer: Option (A) \(b - a + 1\).

NCERT Exemplar Solutions Class 10 – Mathematics – CHAPTER 2: Polynomials – Exercise 2.1 | Detailed Answers