Find all Polynomials `P(x)` which is satisfied that:
`(x-2010)P(x+67)=xP(x)`
(2010 Baltic Way)
Noted that: `2010=30.67`
- If `x=0\leftrightarrow(-2010)P(67)=0\rightarrowP(67)=0`
- If `x=2010\leftrightarrow0P(2007)=2010P(2010)\rightarrowP(2010)=0`
- If `x=67\leftrightarrow(67-2010)P(2.67)=67P(67)\rightarrowP(2.67)=0`
- If `x=2.67\leftrightarrow(2.67-2010)P(3.67)=2.67P(2.67)=0\rightarrowP(3.67)=0`
we will prove this statement by Mathematics Induction
For all `k\inn` and `1\leqn\leq30` we will prove `P(k.67)=0`
`k=0\rightarrowP(0)=0` It is true for `k=0`
We are assuming that's true with `k=n\rightarrowP(n.67)=0``(*)`
We will prove It is true till `k=n+1\rightarrowP[(n+1)67]=0`?
From: `(x-2010)P(x+67)=xP(x)`
Then, `(n.67-2010)P(n.67+67)=n.67P(n.67)=0` Because from our assuming!`(*)`
`\rightarrowP(n.67+67)=0\leftrightarrowP[(n+1).67]=0`
Thus, `P(n.67)=0` for all `1\leqn\leq30`
We can write that:
`P(x)=(x-67)(x-2.67)(x-3.67)........(x-30.67)Q(x)`
Then, `xP(x)=x(x-67)(x-2.67).....(x-30.67)Q(x)` `(1)`
From our hypothesis: `(x-2010)P(x+67)=xP(x)`
But, `(x-2010)P(x+67)=(x-2010)x(x-67)(x-2.67).....(x-29.67)Q(x+67)` `(2)`
From both equations `(1)` and `(2)`: we will see that
`Q(x)=Q(x+67)`
We easily see that `Q(x)=C | C\inR`
Hence, `P(x)=(x-67)(x-2.67)(x-3.67)........(x-30.67)C |C\inR`
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