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Let $$\alpha, \beta$$ be the distinct roots of the equation $$x^2-\left(t^2-5 t+6\right) x+1=0, t \in \mathbb{R}$$ and $$a_n=\alpha^n+\beta^n$$. Then the minimum value of $$\frac{a_{2023}+a_{2025}}{a_{2024}}$$ is

JEE · Math · previous-year question

  1. A.$$-1 / 2$$
  2. B.$$-1 / 4$$correct
  3. C.$$1 / 4$$
  4. D.$$1 / 2$$

Answer

B. $$-1 / 4$$

Explanation

$$\begin{aligned} & x^2-\left(t^2-5 t+6\right) x+1=0 \\ & \therefore a_{2025}-\left(t^2-5 t+6\right) a_{2024}+a_{2023}=0 \\ & \Rightarrow \frac{a_{2025}+a_{2023}}{a_{2024}}=t^2-5 t+6 \\ & =\left(t+\frac{5}{2}\right)^2+\left(\frac{-1}{4}\right) \\ & \text { Minimum value }=\frac{-1}{4} \end{aligned}$$

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