Rewrite in terms of the powers of (x-a) : ptayl

### 2.24.17 Rewrite in terms of the powers of (x-a) : `ptayl`

`ptayl` is used to rewrite a polynomial `P` depending of `x` in terms of the powers of `(x-a)` (`ptayl` means polynomial Taylor)
`ptayl` takes two arguments: a polynomial `P` given by a symbolic expression or by the list of it’s coefficients and a number `a`.
`ptayl` returns the polynomial `Q` such that `Q(x-a)=P(x)`
Input :

`ptayl(x```^```2+2*x+1,2)`

Output, the polynomial Q:

`x```^```2+6*x+9`

Input :

`ptayl([1,2,1],2)`

Output :

`[1,6,9]`

Remark

`P(x)=Q(x-a)`

i.e. for the example :
x2+2x+1=(x−2)2+6(x−2)+9