## Calculus 10th Edition

$f(x)$ has an inverse function.
We use the power rule to find the derivative of $f(x)$. $f'(x) = 5x^4 + 6x^2 = x^2(5x^2+6)$ Both $x^2$ and $5x^2+6$ are always positive so $f'(x)$ is always positive. Therefore, $f(x)$ is strictly monotonic.