Not the exact question you were looking for?

Paste your question to our Mathbee AI Mentor below to get an instant step-by-step solution.

Polynomials
EXAMPLES
CBSE_NCERT_TEXTBOOK
Grade 10

Question:

* : Verify that 3, –1,  are the zeroes of the cubic polynomial p(x) = 3x3 – 5x2 – 11x – 3, and then verify the relationship between the zeroes and the coefficients.

Step-by-Step Solution

Key Concept: Use the Factor Theorem to check each given number as a zero of the polynomial. Then express the cubic as a·(x‑α)(x‑β)(x‑γ) and apply Vieta’s relations: α+β+γ = –b/a, αβ+βγ+γα = c/a, αβγ = –d/a.
1. Check the given numbers as zeroes\
• For \(x = 3\):\
\[p(3)=3(3)^3-5(3)^2-11(3)-3=81-45-33-3=0\]\
Hence \(x=3\) is a zero.\
• For \(x = -1\):\
\[p(-1)=3(-1)^3-5(-1)^2-11(-1)-3=-3-5+11-3=0\]\
Hence \(x=-1\) is a zero.\
• To find the third zero, divide \(p(x)\) by \((x-3)(x+1)\).\
First divide by \(x-3\) (synthetic division):\
\[\begin{array}{c|cccc}
3 & 3 & -5 & -11 & -3 \\
& & 9 & 12 & 3 \\
\hline
& 3 & 4 & 1 & 0 \\
\end{array}\]
Quotient = \(3x^2+4x+1\).\
Factor the quadratic:\
\[3x^2+4x+1 = (3x+1)(x+1)\]\
Hence \(p(x)= (x-3)(x+1)(3x+1)\).\
The remaining zero is obtained from \(3x+1=0\) ⇒ \(x = -\frac{1}{3}\).\
Therefore the three zeroes are \(\alpha=3,\; \beta=-1,\; \gamma=-\frac13\).\

2. Verify Vieta’s relations\
The cubic is of the form \(ax^3+bx^2+cx+d\) with \(a=3,\; b=-5,\; c=-11,\; d=-3\).\
- Sum of zeroes:\
\[\alpha+\beta+\gamma = 3+(-1)+\left(-\frac13\right)=\frac{5}{3}\]\
\[-\frac{b}{a}= -\frac{-5}{3}=\frac{5}{3}\]\
Both are equal, so the first relation holds.\
- Sum of products of zeroes taken two at a time:\
\[\alpha\beta+\beta\gamma+\gamma\alpha = (3)(-1)+(-1)\left(-\frac13\right)+(3)\left(-\frac13\right) = -3+\frac13-1 = -\frac{11}{3}\]\
\[\frac{c}{a}= \frac{-11}{3}= -\frac{11}{3}\]\
Hence the second relation is satisfied.\
- Product of the three zeroes:\
\[\alpha\beta\gamma = 3\times(-1)\times\left(-\frac13\right)=1\]\
\[-\frac{d}{a}= -\frac{-3}{3}=1\]\
The third relation also holds.\

Thus, the numbers \(3, -1, -\frac13\) are indeed the zeroes of \(p(x)\) and they satisfy the standard relationships between zeroes and coefficients for a cubic polynomial.

Correct Answer: The zeroes are \(3, -1, -\frac13\). They satisfy \(\alpha+\beta+\gamma = -\frac{b}{a}=\frac{5}{3}\), \(\alpha\beta+\beta\gamma+\gamma\alpha = \frac{c}{a}= -\frac{11}{3}\), and \(\alpha\beta\gamma = -\frac{d}{a}=1\).
Mathbee AI Mentor (Free Demo)

Confused by the solution? Ask the AI to explain a specific step, tell you where you went wrong, or break down the key trap in this question.

Master Polynomials with Mathbee

Practice this topic under real exam conditions with strict timers, or ask our AI Mentor to explain the concepts step-by-step.

Start Practicing for Free