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If  α, β  and  γ  are the zeros of the polynomial  2x3 − 6x2 − 4x + 30 . then the value of  (αβ + βγ + γα)  isSelect an answerA–2B2C5D–30

Question

If  α, β and  γ are the zeros of the polynomial  2x³ − 6x² − 4x + 30, then the value of  (αβ + βγ + γα) is

Select an answer
A. −2
B. 2
C. 5
D. −30

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Solution

1. Break Down the Problem

We need to find the sum of the products of the roots taken two at a time, which is given by the expression αβ+βγ+γα \alpha\beta + \beta\gamma + \gamma\alpha for the polynomial 2x36x24x+30 2x^3 - 6x^2 - 4x + 30 .

2. Relevant Concepts

For a cubic polynomial in the form: ax3+bx2+cx+d=0 ax^3 + bx^2 + cx + d = 0 the relationships among the roots (α, β, γ) can be determined using Vieta's formulas:

  • Sum of the roots: α+β+γ=ba \alpha + \beta + \gamma = -\frac{b}{a}
  • Sum of the product of the roots taken two at a time: αβ+βγ+γα=ca \alpha\beta + \beta\gamma + \gamma\alpha = \frac{c}{a}
  • Product of the roots: αβγ=da \alpha\beta\gamma = -\frac{d}{a}

For our polynomial:

  • a=2 a = 2
  • b=6 b = -6
  • c=4 c = -4
  • d=30 d = 30

3. Analysis and Detail

Using Vieta's formulas:

  1. The sum of the roots is: α+β+γ=62=62=3 \alpha + \beta + \gamma = -\frac{-6}{2} = \frac{6}{2} = 3
  2. The sum of the products of the roots taken two at a time is: αβ+βγ+γα=42=2 \alpha\beta + \beta\gamma + \gamma\alpha = \frac{-4}{2} = -2
  3. The product of the roots is: αβγ=302=15 \alpha\beta\gamma = -\frac{30}{2} = -15

4. Verify and Summarize

We found the required value: αβ+βγ+γα=2 \alpha\beta + \beta\gamma + \gamma\alpha = -2 which corresponds to option A.

Final Answer

The value of αβ+βγ+γα \alpha\beta + \beta\gamma + \gamma\alpha is 2 \boxed{-2} .

This problem has been solved

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