To determine whether the function is even or odd, use the definitions.
If a function\(f\)satisfies\(f\left( { - x} \right) = f\left( x \right)\)for every number\(x\)in its domain,
then\(f\)is called an even function.
If a function\(f\)satisfies\(f\left( { - x} \right) = - f\left( x \right)\)for every number\(x\)in its domain,
then\(f\)is called an odd function.
Replace\(x\)with\( - x\), in\(f\left( x \right)\).
\(\begin{array}{l}f\left( { - x} \right) = 1 + 3{\left( { - x} \right)^3} - {\left( { - x} \right)^5}\\\;\;\;\;\;\,\,\,\,\, = 1 - 3{x^3} + {x^5}\end{array}\)
The function is neither\(f\left( { - x} \right) \ne f\left( x \right)\)nor\(f\left( { - x} \right) \ne - f\left( x \right)\), so the given functionis neither even nor odd.
Therefore, the function\(f\left( x \right) = 1 + 3{x^3} - {x^5}\)is neither even nor odd.