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Let us define a sequence  (an)n≥1(a_n)_{n \geq 1}(an​)n≥1​​  of real numbers to be a Fibonacci-like sequence if ​an=an−1+an−2,n≥3.a_n = a_{n
Question

Let us define a sequence  (an)n1(a_n)_{n \geq 1}​  of real numbers to be a Fibonacci-like sequence if

an=an1+an2,n3.a_n = a_{n-1} + a_{n-2}, \quad n \geq 3.​​

What is the dimension of the R\mathbb{R}​ -vector space of Fibonacci-like sequences?

A.

1

B.

2

C.

Infinite nd countable.

D.

Infinite and uncountable.

Correct option is B

If an=an1+an2, n3a_n = a_{n-1} + a_{n-2}, \; n \geq 3​​ ,
the terms can be written as:

a3=a2+a1a4=a3+a2a5=a4+a3an=an1+an2.a_3 = a_2 + a_1 \\[10pt]a_4 = a_3 + a_2 \\[10pt]a_5 = a_4 + a_3 \\\vdots\\a_n = a_{n-1} + a_{n-2} .

Substituting values, the equations become:


a3=a2+a1,a4=a2+a1+a2a5=a2+a1+a2+a2,a_3 = a_2 + a_1,\\[10pt]a_4 = a_2 + a_1 + a_2\\[10pt]a_5 = a_2 + a_1 + a_2 + a_2,\\\vdots​​

and so on.

As all terms can be generated by  a1a_1​  and  a2a_2​, the dimension of the vector space will be 2.

Option (B) is correct.\implies \text{Option (B) is correct.}​​

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