Is r(t)\displaystyle {r}{\left({t}\right)} represented in the list of ordered pairs below a function?

r(t)={(3,9),(4,6),(5,10),(6,9),(7,4),(8,7)}\displaystyle {r}{\left({t}\right)}={\left\lbrace{\left({3},{9}\right)},{\left({4},{6}\right)},{\left({5},-{10}\right)},{\left({6},-{9}\right)},{\left({7},{4}\right)},{\left({8},-{7}\right)}\right\rbrace}