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Why sinxcos2x = (sin3x - sinx)*0.5

  • Thread starter fiziksfun
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  • #1
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can someone please show me why sinxcos2x = (sin3x - sinx)*0.5

I've been working on it for thirty minutes
 

Answers and Replies

  • #2
311
1


can u expand sin(3x) ?? and cos(2x)

just simplify both sides..and u'll get it..
 
  • #3
290
2


You should use the identities

[tex]\cos{2\theta} = 1-2\sin^2{\theta}[/tex]

[tex]\sin{3\theta} = 3\sin{\theta} - 4\sin^3{\theta}[/tex]

Perhaps you were putting these identities in terms of cosines. When possible, stick with as few trig functions as possible and replace the [tex]\cos^2{\theta}[/tex] with [tex]1-\sin^2{\theta}[/tex] or vice versa.
 
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