NCERT Exemplar Solutions
Class 10 - Mathematics - CHAPTER 2: Polynomials - Exercise 2.1
Question 5

Question.  5

Given that one of the zeroes of the cubic polynomial \(ax^3+bx^2+cx+d\) is zero, the product of the other two zeroes is

(A)

\(-\dfrac{c}{a}\)

(B)

\(\dfrac{c}{a}\)

(C)

0

(D)

\(-\dfrac{b}{a}\)

Detailed Answer with Explanation:

Step 1: Write down the roots.

The polynomial is \(ax^3 + bx^2 + cx + d\).

It is given that one root is \(0\). Let the other two roots be \(\alpha\) and \(\beta\).

Step 2: Use relations between coefficients and roots.

For a cubic polynomial \(ax^3 + bx^2 + cx + d\) with roots \(r_1, r_2, r_3\):

\(r_1 + r_2 + r_3 = -\dfrac{b}{a}\)

\(r_1r_2 + r_2r_3 + r_3r_1 = \dfrac{c}{a}\)

\(r_1r_2r_3 = -\dfrac{d}{a}\)

Step 3: Substitute the known root.

Take \(r_1 = 0\), \(r_2 = \alpha\), \(r_3 = \beta\).

Then

\(r_1r_2 + r_2r_3 + r_3r_1 = 0 \cdot \alpha + \alpha\beta + 0 \cdot \beta\)

\(= \alpha\beta\).

Step 4: Compare with the formula.

We know \(r_1r_2 + r_2r_3 + r_3r_1 = \dfrac{c}{a}\).

So \(\alpha\beta = \dfrac{c}{a}\).

Answer: The product of the other two zeroes is \(\dfrac{c}{a}\).

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