Visual Derivation of a Trigonometric Identity
This Demonstration gives a visual derivation of a trigonometric relation between the tangents of any three angles whose sum is .
There are a considerable number of trigonometric identities involving angles whose sum is . 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 .
 CTK Wiki Math. "Advanced Identities." (Oct 7, 2019) www.cut-the-knot.org/wiki-math/index.php?n=Trigonometry.AdvancedIdentities.
 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.