Which of the following functions is an odd
function

If $f\left(x\right)=x^4-2x^2$ then $f(-x)=(-x{)}^4-2(-x{)}^2=$

$x^4-2x^2=f\left(x\right)$.Hence $f$ is an even function. If $u\left(x\right)=x-x^2$

then $u(-x)=x-x^2$ so $u$ is neither even nor an odd function

$p\left(x\right)=\mathrm{cbs}x,p(-x)=\cos (-x)=\cos x=p\left(x\right)$ so $p$ is even

function. If $s\left(x\right)=x-\frac{x^3}{6}+\frac{x^5}{40}$ then$s(-x)=-x-\frac{x^3}{6}-\frac{x^5}{40}=$

$-\left(x-\frac{x^3}{6}+\frac{x^5}{40}\right)=-s\left(x\right)$ so $s$ is an odd function