I really need an answer-Derive trig identity

  • Thread starter Dainy
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  • #1
Dainy
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undefinedundefinedundefinedneed help=====)
(sin2x+sin4x)/(cos2x+cos4x)=tan3x
 

Answers and Replies

  • #2
VietDao29
Homework Helper
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You can use these to prove that trig identity:
[tex]\cos \alpha + \cos \beta = 2 \cos \frac{\alpha + \beta}{2} \cos \frac{\alpha - \beta}{2}[/tex]
[tex]\cos \alpha - \cos \beta = - 2 \sin \frac{\alpha + \beta}{2} \sin \frac{\alpha - \beta}{2}[/tex]
[tex]\sin \alpha + \sin \beta = 2 \sin \frac{\alpha + \beta}{2} \cos \frac{\alpha - \beta}{2}[/tex]
[tex]\sin \alpha - \sin \beta = 2 \cos \frac{\alpha + \beta}{2} \sin \frac{\alpha - \beta}{2}[/tex]
Choose 2 of the above equations, and use them.
Can you go from there?
Viet Dao,
 

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