\[\left( - a^{2}b^{3}c^{4} \right)^{7} =\]
\[= ( - 1)^{7}\left( a^{2} \right)^{7}\left( b^{3} \right)^{7}\left( c^{4} \right)^{7} =\]
\[= - a^{14}b^{21}c^{28}.\]