Answer
$f(x) = x^{2}$
Work Step by Step
This function passes the horizontal line test on the interval $(-\infty,0]$ but not on $(-\infty,\infty)$.
You can help us out by revising, improving and updating this answer.
Update this answerAfter you claim an answer you’ll have 24 hours to send in a draft. An editor will review the submission and either publish your submission or provide feedback.