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FM June 2023 p13 q03
4215
The equation \(x^4 - x^2 + 2x + 5 = 0\) has roots \(\alpha, \beta, \gamma, \delta\).
(a) Find a quartic equation whose roots are \(\alpha^2, \beta^2, \gamma^2, \delta^2\) and state the value of \(\alpha^2 + \beta^2 + \gamma^2 + \delta^2\).
(b) Find the value of \(\frac{1}{\alpha^2} + \frac{1}{\beta^2} + \frac{1}{\gamma^2} + \frac{1}{\delta^2}\).
(c) Find the value of \(\alpha^4 + \beta^4 + \gamma^4 + \delta^4\).
Solution
(a) Let \(y = x^2\), so \(x = y^{\frac{1}{2}}\). Substitute into the original equation:
\(y^2 - y + 2y^{\frac{1}{2}} + 5 = 0\).
Rearrange and square both sides to eliminate the square root:
\((2y^{\frac{1}{2}})^2 = (-y^2 + y - 5)^2\).
Expand and simplify to obtain:
\(y^4 - 2y^3 + 11y^2 - 14y + 25 = 0\).
The value of \(\alpha^2 + \beta^2 + \gamma^2 + \delta^2\) is 2.
(b) Using the relation \(\alpha^2 \beta^2 \gamma^2 \delta^2 = 25\), we have: