Let R be a commutative rng and consider R[x]

Define: \(\displaystyle\phi:{R}\to{R}{\left[{x}\right]}\) by \(\displaystyle{r}\mapsto{r}\)

Here, clearly we can say that \(\displaystyle\phi\) is one-to-one and homomorphism

Now, \(\displaystyle\phi{\left({R}\right)}\) is subsring of R[x] since it is the imag of a homomorphism

Then \(\displaystyle\phi{\left({R}\right)}\) is subsring of R[x] isomorphic to R

Define: \(\displaystyle\phi:{R}\to{R}{\left[{x}\right]}\) by \(\displaystyle{r}\mapsto{r}\)

Here, clearly we can say that \(\displaystyle\phi\) is one-to-one and homomorphism

Now, \(\displaystyle\phi{\left({R}\right)}\) is subsring of R[x] since it is the imag of a homomorphism

Then \(\displaystyle\phi{\left({R}\right)}\) is subsring of R[x] isomorphic to R