~~Hi, ~~I ~~have a multi-variable polynomial whose coefficients are algebraic numbers. For a start, ~~edited my question and put the answer I found, so this solves my problem!

My problem was: take a field " E " generated by " r " (here, "r" is a root of X^3 - 2 ) and 3 variables " b0 , b1 , b2 ".

I want to ~~convert it into a single - variable polynomial whose variable is the constant - algebraic number. Here is a simple example. ~~

```
Q.<x>=QQ[]
F.<r>=NumberField(x^2-2) # this is the produce the element " A = b0 + r * b1 + r^2 * b2 " and it's square:
```A^2 = b0^2 + (2*r) * b0 * b1 + (r^2) * b1^2 + (2*r^2) * b0 * b2 + 4 * b1 * b2 + (2*r) * b2^2

and express A and A^2 in terms of the basis "( 1 , r , r^2 )" so that the result becomes:

A^2 = r^2 ( b1^2 + 2 b0 * b2 ) + r ( 2 b0 * b1 + 2 b2^2 ) + ( b0^2 + b2^2 + b1 * b2 )

`The solution was simply to define the number field `~~of the ~~as an extension of the ring of coefficients ~~of a polynomial, just allowed to be r or 2
R.<x,y,z,t> =PolynomialRing(F)
~~

P = sum( [ R.gens()[i] and the other way round! Good!

B=PolynomialRing(E,3,'b');

v=B.gens()

E.<r>=B.extension(x^3-2)

A^2=sum( [v[i] * r^i for ~~ ~~i ~~ ~~in ~~ range(4) ~~range(3) ] ~~); # P = x + r* y +r^2 * z + r^3 * t~~

The output is: P(x,y,t) = x + (r)*y )*

* *gives me the solution:

*(b1^2 + 2*z + (2r)*t

I would like to get P(r) = (y + 2t) * r + (x+2*t)*b0*b2)*r^2 + (2*b0*b1 + 2*b2^2)*r + b0^2 + 4*b1*b2

result expressed in terms of powers of "r".