\[8x^{3}y^{4} \cdot \left( - 0,5x^{2}y^{5} \right)^{3} =\]
\[= 8x^{3}y^{4} \cdot \left( - 0,125x^{6}y^{15} \right) = - x^{9}y^{19}\text{.\ }\]