Multiline equation write form in text cell?

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Is there a way to write equation within text cell as few lines?

For example this:

$f(x) = y^x$

renders normally, but this:

$f(x)
=
y^x$

renders as plain text. I wan it to be rendered in the same way as first one.

P.S. I am new to latex, so trying to find a way to make complex equation in latex more readable (may be there is a better way to do it than splitting it to a few lines?).