Medium MCQ +4 / -1 PYQ · JEE Mains 2024

If $\alpha, \beta$ are the roots of the equation, $x^2-x-1=0$ and $S_n=2023 \alpha^n+2024 \beta^n$, then :

  1. A $2 S_{12}=S_{11}+S_{10}$
  2. B $S_{12}=S_{11}+S_{10}$ Correct answer
  3. C $S_{11}=S_{10}+S_{12}$
  4. D $2 S_{11}=S_{12}+S_{10}$

Solution

<p>$$\begin{aligned} & x^2-x-1=0 \\ & S_n=2023 \alpha^n+2024 \beta^n \\ & S_{n-1}+S_{n-2}=2023 \alpha^{n-1}+2024 \beta^{n-1}+2023 \alpha^{n-2}+2024 \beta^{n-2} \\ & =2023 \alpha^{n-2}[1+\alpha]+2024 \beta^{n-2}[1+\beta] \\ & =2023 \alpha^{n-2}\left[\alpha^2\right]+2024 \beta^{n-2}\left[\beta^2\right] \\ & =2023 \alpha^n+2024 \beta^n \\ & S_{n-1}+S_{n-2}=S_n \\ & P_{u t} n=12 \\ & S_{11}+S_{10}=S_{12} \end{aligned}$$</p>

About this question

Subject: Mathematics · Chapter: Complex Numbers and Quadratic Equations · Topic: Complex Numbers and Argand Plane

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