I have two algebraic numbers defined by minimal polynomials:

    x, z = symbols('x, z')
    p = Poly((x-1)*(x-2)*(x-3)*(x-4))
    q = Poly((x-5)*(x-6)*(x-7)*(x-8))

and I would like to compute the sum of these numbers. I 
[found](http://math.stackexchange.com/a/155132/327863) that I need to 
"`z=x+y` is a root of the resultant of `P(x)` and `Q(z−x)` (where we take 
this resultant by regarding `Q` as a polynomial in only `x`)".

I'm totally new to all this algebraic numbers thing so I don't quite 
understand the advice but I tried:

    resultant(p, q.subs(x, z-x))

but then I got stuck. Please, could someone explain to me:

- I would like to see the steps that lead to the computation of desired 
minimal polynomial with the help of resultant. I think I defined the two 
numbers properly but I don't know how to express that `Q(z−x)`.

- As it stands now, the `resultant` function returns bivariate polynomial 
but I would've assumed that the resulting minimal polynomial should be 
univariate. How do I get rid of the second variable?

- The above link also says "`P(x) = Q(y) = 0`". Does it mean that `p` and 
`q` can't be both `Poly((x-1)*(x-2)*(x-3)*(x-4))`? What if I would like to 
add the same two numbers?

Thank you very much in advance!

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