AQA FP2 2009 January — Question 4

Exam BoardAQA
ModuleFP2 (Further Pure Mathematics 2)
Year2009
SessionJanuary
TopicRoots of polynomials

4 It is given that \(\alpha , \beta\) and \(\gamma\) satisfy the equations $$\begin{aligned} & \alpha + \beta + \gamma = 1
& \alpha ^ { 2 } + \beta ^ { 2 } + \gamma ^ { 2 } = - 5
& \alpha ^ { 3 } + \beta ^ { 3 } + \gamma ^ { 3 } = - 23 \end{aligned}$$
  1. Show that \(\alpha \beta + \beta \gamma + \gamma \alpha = 3\).
  2. Use the identity $$( \alpha + \beta + \gamma ) \left( \alpha ^ { 2 } + \beta ^ { 2 } + \gamma ^ { 2 } - \alpha \beta - \beta \gamma - \gamma \alpha \right) = \alpha ^ { 3 } + \beta ^ { 3 } + \gamma ^ { 3 } - 3 \alpha \beta \gamma$$ to find the value of \(\alpha \beta \gamma\).
  3. Write down a cubic equation, with integer coefficients, whose roots are \(\alpha , \beta\) and \(\gamma\).
  4. Explain why this cubic equation has two non-real roots.
  5. Given that \(\alpha\) is real, find the values of \(\alpha , \beta\) and \(\gamma\).