hi! I have problems with demostration

Show that there is an isomorphism of fields:

$\displaystyle \mathbb{R} \left [ x \right ] / (x^2+1) \cong \mathbb{R} \left [ x \right ] / (x^2+x+1) $

Hint: Both are isomorphic to $\displaystyle \mathbb{C}$

I do not know how to use the hint

Thanks