Spezzare un’equazione (frazione) su più righe

Salve e buon anno a tutti.

Brevemente: vorrei spezzare questa formula, ad esempio, su più righe

$
\cfrac{g_{\text{m3}} r_{3 a} r_{\text{dnp}} \left(r_{\text{d7}} \left(g_{\text{mp}}+S c_n \left(-1+g_{\text{mp}} r_n \right)\right) + g_{\text{mn}}
\left(r_{\text{d7}} \left(1+S c_n r_n \right) + r_d \left( 1+S c_n \left( r_{\text{d7}} + r_n \right)\right)\right) + S c_p \left(r_d \left(1+S c_n \left(r_{\text{d7}}+r_n \right)\right)
\left(-1+g_{\text{mn}} r_p \right)+r_ {\text{d7}} \left(-1+g_{\text{mn}} r_p+g_{\text{mp}} r_p+S c_n \left(-r_p+r_n \left(-1+g_{\text{mn}} r_p+g_{\text{mp}}
r_p \right)\right)\right)\right)\right)}{2 \left(r_ {\text{d7}} \left(1+S c_p \left(r_{\text{dnp}}+r_p \right)+S c_n \left(r_n \left(1+S c_p r_p \right)+r_ {\text{dnp}} \left(1+S c_p \left(r_n+r_p \right)\right)\right)\right)+r_d \left(1+S c_p r_{\text{dnp}}+S c_p r_p+S c_n \left(r_n \left(1+S c_p r_p \right)+r_ {\text{dnp}}
\left(1+S c_p \left(r_n+r_p \right)\right)+r_ {\text{d7}} \left(1+g_{\text{mp}} r_{\text{dnp}}+S c_p \left(r_{\text{dnp}}+r_p+g_{\text{mp}} r_{\text{dnp}}
r_p \right)\right)\right)\right)+r_ {3 a} \left(1+S c_{\text{t1}} r_d+S c_n r_{\text{d7}}+S c_{\text{t1}} r_{\text{d7}}+S^2 c_n c_{\text{t1}} r_d r_{\text{d7}}+S
c_n r_{\text{dnp}}+S^2 c_n c_{\text{t1}} r_d r_{\text{dnp}}+S^2 c_n c_{\text{t1}} r_{\text{d7}} r_{\text{dnp}}+S c_n g_{\text{mn}} r_{\text{d7}}
r_{\text{dnp}}+S c_n g_{\text{mp}} r_{\text{d7}} r_{\text{dnp}}+S^2 c_n c_{\text{t1}} g_{\text{mp}} r_d r_{\text{d7}} r_{\text{dnp}}+S c_n r_n+S^2
c_n c_{\text{t1}} r_d r_n+S^2 c_n c_{\text{t1}} r_{\text{d7}} r_n+S c_p \left(r_{\text{dnp}}+S c_n r_{\text{dnp}} r_n+r_p+S c_n r_{\text{dnp}} r_p+S
c_n r_n r_p+r_ {\text{d7}} \left(\left(1+g_{\text{mn}} r_{\text{dnp}}+g_{\text{mp}} r_{\text{dnp}}\right) \left(1+S c_n \left(r_n+r_p \right)\right)+S
c_ {\text{t1}} \left(\left(1+S c_n r_n \right) r_p + r_{\text{dnp}} \left(1+S c_n \left(r_n+r_p \right)\right)\right)\right)+r_d \left(1+S c_{\text{t1}}
r_{\text{dnp}}+g_{\text{mn}} r_{\text{dnp}}+S c_{\text{t1}} r_p+S c_n \left(r_n \left(1+S c_{\text{t1}} r_p \right)+r_ {\text{dnp}} \left(1+g_{\text{mn}}
r_n + S c_{\text{t1}} \left(r_n+r_p \right) \right) + r_{\text{d7}} \left(1+g_{\text{mn}} r_{\text{dnp}}+g_{\text{mp}} r_{\text{dnp}} + S c_ {\text{t1}} \left(r_{\text{dnp}}+r_p+g_{\text{mp}}
r_{\text{dnp}} r_p \right) \right) \right) \right) \right) \right) \right)}
$

Premetto che ho cercato anche di ruotare la pagina e cambiarne il formato (e su questo avrei altre domande) con

\usepackage{pdflscape}
\begin{landscape}
…
\end{landscape}

per guadagnare spazio nonché di usare i comandi come split, aligned, ecc ma senza risultato.

Potrei tentare di riscriverla in modo più “decente” ma così è la forma rischiesta.

Saluti e grazie come al solito

Stefano