Reciprocal sum for a cubic

Reciprocal sum for a cubic

IB Year 6 | Grade 12

The roots of the equation \(3x^3+6x^2-2x-4=0\) are \(\alpha\), \(\beta\) and \(\gamma\).

  1. Write down the values of \(\alpha+\beta+\gamma\), \(\alpha\beta+\beta\gamma+\gamma\alpha\) and \(\alpha\beta\gamma\).
  2. Hence find the value of \(\dfrac{1}{\alpha}+\dfrac{1}{\beta}+\dfrac{1}{\gamma}\).

Solution:

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Answer:(a) \(-2,\ -\frac{2}{3},\ \frac{4}{3}\) (b) \(-\frac{1}{2}\)

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