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Question Number 4720 by prakash jain last updated on 29/Feb/16

Prove or counterexample that if a finite number   of terms of a series are given then a infinite number  of formulas for n^(th)  term exists which satisfy  the given finite number of terms.  For example  33,9,33,44,?  4 terms are given if a_n =f(n) then there are  infinite number of distinct f_k (n) such for  all k.  f_k (1)=a_1 ,f_k (2)=a_2 ,f_k (3)=a_3 ,f_k (4)=a_4   and there exists m∈N such thatf_k (m)≠f_j (m)   if k≠j

$$\mathrm{Prove}\:\mathrm{or}\:\mathrm{counterexample}\:\mathrm{that}\:\mathrm{if}\:\mathrm{a}\:\mathrm{finite}\:\mathrm{number}\: \\ $$$$\mathrm{of}\:\mathrm{terms}\:\mathrm{of}\:\mathrm{a}\:\mathrm{series}\:\mathrm{are}\:\mathrm{given}\:\mathrm{then}\:\mathrm{a}\:\mathrm{infinite}\:\mathrm{number} \\ $$$$\mathrm{of}\:\mathrm{formulas}\:\mathrm{for}\:{n}^{{th}} \:\mathrm{term}\:\mathrm{exists}\:\mathrm{which}\:\mathrm{satisfy} \\ $$$$\mathrm{the}\:\mathrm{given}\:\mathrm{finite}\:\mathrm{number}\:\mathrm{of}\:\mathrm{terms}. \\ $$$$\mathrm{For}\:\mathrm{example} \\ $$$$\mathrm{33},\mathrm{9},\mathrm{33},\mathrm{44},? \\ $$$$\mathrm{4}\:\mathrm{terms}\:\mathrm{are}\:\mathrm{given}\:\mathrm{if}\:{a}_{{n}} ={f}\left({n}\right)\:\mathrm{then}\:\mathrm{there}\:\mathrm{are} \\ $$$$\mathrm{infinite}\:\mathrm{number}\:\mathrm{of}\:\mathrm{distinct}\:{f}_{{k}} \left({n}\right)\:\mathrm{such}\:\mathrm{for} \\ $$$$\mathrm{all}\:{k}. \\ $$$${f}_{{k}} \left(\mathrm{1}\right)={a}_{\mathrm{1}} ,{f}_{{k}} \left(\mathrm{2}\right)={a}_{\mathrm{2}} ,{f}_{{k}} \left(\mathrm{3}\right)={a}_{\mathrm{3}} ,{f}_{{k}} \left(\mathrm{4}\right)={a}_{\mathrm{4}} \\ $$$$\mathrm{and}\:\mathrm{there}\:\mathrm{exists}\:{m}\in\mathbb{N}\:\mathrm{such}\:\mathrm{that}{f}_{{k}} \left({m}\right)\neq{f}_{{j}} \left({m}\right)\: \\ $$$$\mathrm{if}\:{k}\neq{j} \\ $$

Answered by 123456 last updated on 29/Feb/16

if we have f such that for m terms  a_n =f(n)  n∈{1,...,m}  we can generate other function by  h(n)=C(x−1)...(x−m)g(x)+f(x)  for any g and C

$$\mathrm{if}\:\mathrm{we}\:\mathrm{have}\:{f}\:\mathrm{such}\:\mathrm{that}\:\mathrm{for}\:{m}\:\mathrm{terms} \\ $$$${a}_{{n}} ={f}\left({n}\right)\:\:{n}\in\left\{\mathrm{1},...,{m}\right\} \\ $$$$\mathrm{we}\:\mathrm{can}\:\mathrm{generate}\:\mathrm{other}\:\mathrm{function}\:\mathrm{by} \\ $$$${h}\left({n}\right)={C}\left({x}−\mathrm{1}\right)...\left({x}−{m}\right){g}\left({x}\right)+{f}\left({x}\right) \\ $$$$\mathrm{for}\:\mathrm{any}\:{g}\:\mathrm{and}\:{C} \\ $$

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