Thackeray, Henry (Maya) Robert2023-04-212023Thackeray, H.R. 2022, 'Dissection-like proofs of the law of cosines', Mathematics Magazine, vol. 96, no. 2, pp. 120-129, https://doi.org/10.1080/0025570X.2023.2167407.0025-570X (print)1930-0980 (online)10.1080/0025570X.2023.2167407http://hdl.handle.net/2263/90412Inspired by arguments illustrating the Pythagorean theorem, this paper gives six interrelated dissection-like proofs of the law of cosines. Each proof treats the acute- and obtuse-angle cases together, and uses a trigonometric double-angle formula. Some of the proofs assume the Pythagorean theorem.en© 2023 Mathematical Association of America. This is an electronic version of an article published in Mathematics Magazine, vol. 96, no. 2, pp. 120-129, 2023, https://doi.org/10.1080/0025570X.2023.2167407. Mathematics Magazine is available online at: http://www.tandfonline.com/loi/umma20.Dissection-like proofsLaw of cosinesPythagorean theoremPostprint Article