\[3x^{3} - 5x^{2} + 2x - 15;\]
\[x = - x:\]
\[3 \cdot ( - x)^{3} - 5 \cdot ( - x)^{2} + 2 \cdot ( - x) - 15 =\]
\[= - 3x^{3} - 5x^{2} - 2x - 15.\]