PROOF WITHOUT WORDS: TANGENT SUM IDENTITY
Keywords:
tangent sum identity.DOI:
https://doi.org/10.17654/0973563125007Abstract
A visual proof of the tangent sum identity
$$
\tan (\alpha+\beta)=\frac{\tan \alpha+\tan \beta}{1-\tan \alpha \tan \beta}
$$
is given.
References
R. Nelsen, Proofs Without Words, MAA, Washington DC, 1993, pp. 34-35.
Y. Kobayashi, Proofs without words: tangent double angle identity, College Math. J. 44 (2013), 47.
L. Wang, Proofs without words: sine sum identity, College Math. J. 45 (2014), 190.
L. Wang, Proofs without words: cosine difference identity, College Math. J. 45 (2014), 370.
L. Wang, Proofs without words: sine difference identity, Far East Journal of Mathematical Education 26(2) (2024), 123-124.
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