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单词 DoubleAngleIdentity
释义

double angle identity


The double angle identities are

sin(2x)=2sinxcosx(1)
cos(2x)=cos2x-sin2x=2cos2x-1=1-2sin2x(2)
tan(2x)=2tanx1-tan2x(3)

These are all derived from their respective trigonometric addition formulas. For example,

sin(2x)=sin(x+x)
=sinxcosx+cosxsinx
=2sinxcosx

The formula for cosine follows similarly, and the formula tangentPlanetmathPlanetmathPlanetmath is derived by taking the ratio of sine to cosine, as always.

The double angle identities can also be derived from the de Moivre identityMathworldPlanetmath.

Titledouble angle identity
Canonical nameDoubleAngleIdentity
Date of creation2013-03-22 12:14:31
Last modified on2013-03-22 12:14:31
OwnerWkbj79 (1863)
Last modified byWkbj79 (1863)
Numerical id16
AuthorWkbj79 (1863)
Entry typeTheorem
Classificationmsc 26A09
Classificationmsc 33B10
Synonymdouble-angle identity
Synonymdouble angle formula
Synonymdouble-angle formula
Synonymdouble angle formulae
Synonymdouble-angle formulae
Related topicDeMoivreIdentity
Related topicAngleSumIdentity
Related topicAdditionFormulasForSineAndCosine
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更新时间:2025/5/4 22:27:17