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Presume that $α_1$ and $α_2$ are solutions to the quadratic function, prove that $α_1^n$ and $α_2^n$ fulfill the recursive formula

Quadratic function: $x^2 = bx + c$

Recursive formula: $ a_{n+2} = ba_{n+1} + ca_n$

I'm honestly very lost on this one

JohnDoe
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1 Answers1

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Multiply $\alpha^2 = b\alpha + c$ by $\alpha^n$ to get $\alpha^{n+2} = b\alpha^{n+1} + c\alpha^n$ for all $n \in \mathbb N$.

lhf
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  • Ah I was making it way more complicated than I had to...

    Ah I was making it way more complicated than I had to...

    If I could ask a follow up question:

    Presume that $α_1 ≠ α_2$ and that $a_1$ and $a_2$ are given. Prove that there is always coefficients $r$ and $s$ so that:

    $rα_1 + sα_2 = a_1$

    , $rα_1^2 + sα_2^2 = a_2$

    am I supposed to use the recursion condition to prove this?

    – JohnDoe Feb 01 '18 at 15:49
  • @JohnDoe, ask a separate question. – lhf Feb 01 '18 at 18:17