\[1)\ y = 2x^{2} - 1:\]
\[D(x) = ( - \infty;\ + \infty);\]
\[y( - x) = 2( - x)^{2} - 1 =\]
\[= 2x^{2} - 1 = y(x).\]
\[Ответ:\ \ четная.\]
\[2)\ y = x - x^{3};\]
\[D(x) = ( - \infty;\ + \infty);\]
\[y( - x) = - x - ( - x)^{3} =\]
\[= - x + x^{3} = - y(x).\]
\[Ответ:\ \ нечетная.\]
\[3)\ y = x^{5} - \frac{1}{x}:\]
\[D(x) = ( - \infty;\ 0) \cup (0;\ + \infty);\]
\[y( - x) = ( - x)^{5} - \frac{1}{- x} =\]
\[= - x^{5} + \frac{1}{x} = - y(x).\]
\[Ответ:\ \ нечетная.\]
\[4)\ y = \frac{\sin x}{x}:\]
\[D(x) = ( - \infty;\ 0) \cup (0;\ + \infty);\]
\[y( - x) = \frac{\sin( - x)}{- x} = \frac{- \sin x}{- x} =\]
\[= \frac{\sin x}{x} = y(x).\]
\[Ответ:\ \ четная.\]