Verify whether there exists a polynomial [tex]f(x)[/tex] such that [tex]f(f(x))=x^2-x+1[/tex], and find [tex]f(0)[/tex].

By Ava

Verify whether there exists a polynomial [tex]f(x)[/tex] such that [tex]f(f(x))=x^2-x+1[/tex], and find [tex]f(0)[/tex].

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Ava

2 thoughts on “Verify whether there exists a polynomial [tex]f(x)[/tex] such that [tex]f(f(x))=x^2-x+1[/tex], and find [tex]f(0)[/tex].”

  1. [tex]\large\underline{\sf{Given- }}[/tex]

    [tex] \: \: \: \: \: \bull \: \sf \: \: f(f(x)) = {x}^{2} – x + 1[/tex]

    [tex]\large\underline{\sf{To\:Find – }}[/tex]

    [tex] \: \: \: \: \: \bull \: \sf \: \: f(0)[/tex]

    [tex]\large\underline{\sf{Solution-}}[/tex]

    Given that

    [tex]\rm :\longmapsto\:\sf \: \: f(f(x)) = {x}^{2} – x + 1 – – – (1)[/tex]

    • Put x = 0, in equation (1), we get

    [tex]\rm :\longmapsto\:\sf \: \: f(f(0)) = {0}^{2} – 0 + 1[/tex]

    [tex]\rm :\longmapsto\:\sf \: \: f(f(0)) =1 – – – (2)[/tex]

    • Put x = 1, in equation (1) we get

    [tex]\rm :\longmapsto\:\sf \: \: f(f(1)) = {1}^{2} – 1 + 1[/tex]

    [tex]\rm :\longmapsto\:\sf \: \: f(f(1)) = 1 – – – (3)[/tex]

    Hᴇɴᴄᴇ,

    ➢ Pair of points of the given equation are shown in the below table.

    [tex]\begin{gathered}\boxed{\begin{array}{c|c} \bf x & \bf f(f(x)) \\ \frac{\qquad \qquad}{} & \frac{\qquad \qquad}{} \\ \sf 0 & \sf 1 \\ \\ \sf 1 & \sf 1 \end{array}} \\ \end{gathered}[/tex]

    Now,

    • Again we have given that

    [tex]\rm :\longmapsto\:\sf \: \: f(f(x)) = {x}^{2} – x + 1[/tex]

    [tex]\rm :\longmapsto\: \red{ \bf \: Put \: x \: = \: f(x), \: we \: get}[/tex]

    [tex]\rm :\longmapsto\:\sf \: \: f(f(f(x))) = {f(x)}^{2} – f(x) + 1 – – (4)[/tex]

    [tex]\rm :\longmapsto\: \blue{ \bf \: Put \: x = 0, \: we \: get}[/tex]

    [tex]\rm :\longmapsto\:\sf \: \: f(f(f(0))) = {f(0)}^{2} – f(0) + 1[/tex]

    [tex]\rm :\longmapsto\:\sf \: \: f(1) = {f(0)}^{2} – f(0) + 1 – – – (5)[/tex]

    [tex] \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \boxed{ \because \bf \: f(f(0)) = 1}[/tex]

    Now,

    • if we get the value of f(1), we are able to find f(0)

    So,

    • Put x = 1, in equation (4), we get

    [tex]\rm :\longmapsto\:\sf \: \: f(f(f(1))) = {f(1)}^{2} – f(1) + 1 [/tex]

    [tex]\rm :\longmapsto\:\sf \: \: f(1) = {f(1)}^{2} – f(1) + 1 \: \: \{\because \: f(f(1)) = 1 \}[/tex]

    [tex]\rm :\longmapsto\:\sf \: \: {f(1)}^{2} -2 f(1) + 1= 0[/tex]

    [tex]\rm :\longmapsto\: {(f(1) – 1)}^{2} = 0[/tex]

    [tex]\rm :\longmapsto\:f(1) – 1 = 0[/tex]

    [tex]\bf\implies \:f(1) = 1 – – – (6)[/tex]

    On substituting f(1) = 1 in equation (5), we get

    [tex]\rm :\longmapsto\:\sf \: \: \cancel1 = {f(0)}^{2} – f(0) + \cancel1[/tex]

    [tex]\rm :\longmapsto\: {f(0)}^{2} – f(0) = 0[/tex]

    [tex]\rm :\longmapsto\:f(0)\bigg(f(0) – 1 \bigg) = 0[/tex]

    [tex]\bf\implies \:f(0) \: = \: 0 \: \: or \: \: f(0) \: = \: 1[/tex]

    Verification :-

    Case :- 1

    • When f(0) = 0

    Then,

    • Value of f(f(x)) when x = 0, is

    [tex]\rm :\longmapsto\: f(f(0)) = f(0) = 0[/tex]

    [tex]\rm :\longmapsto\:which \: is \: contradiction \: as \: f(f(0)) = 1[/tex]

    So,

    [tex]\bf\implies \:f(0) \: \ne \: 0[/tex]

    Case :- 2

    • When f(0) = 1

    Then

    Value of f(f(x)) when x = 0,is

    [tex]\rm :\longmapsto\: f(f(0)) = f(1) = 1 \: satisfies.[/tex]

    [tex]\bf\implies \:f(0) = 1[/tex]

    [tex] \: \: \: \: \: \: \overbrace{ \underline { \boxed { \bf \therefore \: The \: value \: of \: f(0) = 1}}}[/tex]

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