# Visual Derivation of a Trigonometric Identity

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This Demonstration gives a visual derivation of a trigonometric relation between the tangents of any three angles whose sum is .

Contributed by: Tomas Garza (October 2019)

Open content licensed under CC BY-NC-SA

## Details

There are a considerable number of trigonometric identities involving angles whose sum is [1]. This is not the case for angles whose sum is .

This Demonstration provides a visual derivation of a particular relation among the tangents of three such angles, which is useful in application to certain problems [2].

References

[1] CTK Wiki Math. "Advanced Identities." (Oct 7, 2019) www.cut-the-knot.org/wiki-math/index.php?n=Trigonometry.AdvancedIdentities.

[2] R. B. Nelsen, "Heron's Formula via Proofs without Words," *The College Mathematics Journal*, 32 (4), 2001, p. 291. www.maa.org/programs/faculty-and-departments/classroom-capsules-and-notes/herons-formula-via-proofs-without-words.

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