# Multiply polynomials from different rings

Suppose I take a polynomial from $K[x]$, say $x^2 + 5x$, and another polynomial from $K[y]$, say $y^3$. I want to formally multiply them and get $x^2y^3 + 5xy^3$ as the output.

How can I do that?

Note: `K`

is the finite field of size 4 in `a`

.

My efforts:

```
sage: K.<a> = FiniteField(4)
sage: R_1 = PolynomialRing(K, ['z%s' % p for p in range(1, 3)])
sage: R_2 = PolynomialRing(K, ['x%s' % p for p in range(1, 3)])
sage: pp = R_1.random_element()
sage: pp
(a + 1)*z1^2 + (a)*z1*z2 + (a + 1)*z2 + (a)
sage: qq = R_2.random_element()
sage: qq
x1*x2 + (a + 1)*x2^2 + x1 + 1
```

When I do `pp*qq`

I get the following output

```
unsupported operand parent(s) for *: 'Multivariate Polynomial Ring
in z1, z2 over Finite Field in a of size 2^2' and 'Multivariate Polynomial
Ring in x1, x2 over Finite Field in a of size 2^2'
```