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If α and β are the roots of the quadratic equation 3x² − 4x − 2 = 0, find the value of 4α + 4β / α - β

Mathematics

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Answers

2 parts
i

163\frac{16}{3}

ii

±2103\pm \frac{2\sqrt{10}}{3}

Step-by-step solution

3 steps

The given quadratic equation is 3x2−4x−2=03x^2 - 4x - 2 = 0.
For a quadratic equation in the form ax2+bx+c=0ax^2 + bx + c = 0, the sum of the roots (α+β\alpha + \beta) and the product of the roots (αβ\alpha \beta) are given by Vieta's formulas:
α+β=−ba\alpha + \beta = -\frac{b}{a}
αβ=ca\alpha \beta = \frac{c}{a}

From the given equation, we have a=3a=3, b=−4b=-4, and c=−2c=-2.

Step 1: Calculate the sum and product of the roots.
Sum of roots:

α+β=−−43=43\alpha + \beta = -\frac{-4}{3} = \frac{4}{3}

Product of roots:

αβ=−23\alpha \beta = \frac{-2}{3}

Part i· 1 step

Find the value of 4α+4β4\alpha + 4\beta

  1. Factor out 4 and substitute the sum of roots.

    4α+4β=4(α+β)4\alpha + 4\beta = 4(\alpha + \beta) 4(α+β)=4×434(\alpha + \beta) = 4 \times \frac{4}{3} 4(α+β)=1634(\alpha + \beta) = \frac{16}{3}

    The value is 163\boxed{\frac{16}{3}}.

Part ii

±2103\pm \frac{2\sqrt{10}}{3}

Find the value of α−β\alpha - \beta

  1. Use the identity (α−β)2=(α+β)2−4αβ(\alpha - \beta)^2 = (\alpha + \beta)^2 - 4\alpha\beta.

    Substitute the values of α+β\alpha + \beta and αβ\alpha \beta:

    (α−β)2=(43)2−4(−23)(\alpha - \beta)^2 = \left(\frac{4}{3}\right)^2 - 4\left(\frac{-2}{3}\right) (α−β)2=169+83(\alpha - \beta)^2 = \frac{16}{9} + \frac{8}{3}

    To add the fractions, find a common denominator, which is 9:

    (α−β)2=169+8×33×3(\alpha - \beta)^2 = \frac{16}{9} + \frac{8 \times 3}{3 \times 3} (α−β)2=169+249(\alpha - \beta)^2 = \frac{16}{9} + \frac{24}{9} (α−β)2=16+249(\alpha - \beta)^2 = \frac{16 + 24}{9} (α−β)2=409(\alpha - \beta)^2 = \frac{40}{9}
  2. Take the square root to find α−β\alpha - \beta.

    α−β=±409\alpha - \beta = \pm \sqrt{\frac{40}{9}} α−β=±409\alpha - \beta = \pm \frac{\sqrt{40}}{\sqrt{9}} α−β=±4×103\alpha - \beta = \pm \frac{\sqrt{4 \times 10}}{3} α−β=±2103\alpha - \beta = \pm \frac{2\sqrt{10}}{3}

    The value is ±2103\boxed{\pm \frac{2\sqrt{10}}{3}}.

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