PRANATA, Ricki. Students’ learning results on trigonometry material through Numbered Heads Together cooperative model with mnemonic strategy. Proceedings of English Education International Conference, [S.l.], v. 1, n. 2, p. 276-279, nov. 2016. ISSN 2527-8037. Available at: <http://eeic.unsyiah.ac.id/proceedings/index.php/eeic/article/view/57>. Date accessed: 25 nov. 2020.