#### Answer

$f(x)$ is not one-to-one.

#### Work Step by Step

The function $f(x)=x^4+5$ is not one-to-one because it fails the horizontal line test (even function). We can show that it has the same $y$ value for two different $x$ values:
$f(-1)=(-1)^4+5=1+5=6$
$f(1)=1^4+5=1+5=6$
Thus the function is not one-to-one.