anonymous
  • anonymous
sin8x=8sinxcosxcos2xcos4x proving trig identity?
Mathematics
  • Stacey Warren - Expert brainly.com
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SOLVED
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schrodinger
  • schrodinger
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anonymous
  • anonymous
\[\sin8x=8sinxcosxcos2xcos4x\]
anonymous
  • anonymous
i have LS: sin8x = sin(4x+4x) = 2sin4xcos4x then i have no idea.. should i just keep on expanding? or is there another way of solving this?
TuringTest
  • TuringTest
repeat the process: sin4x=2sin2xcos2x sin2x=2sinxcosx

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anonymous
  • anonymous
just keep doing that? :/ would that even get simplified?
anonymous
  • anonymous
\[ \sin 8x = 2 \sin 4x \cos 4x = 4\sin 2x \cos 2x \cos 4x = 8 \sin x \cos x \cos 2x \cos 4x \]
TuringTest
  • TuringTest
not sure if you want to call it 'simplified', but it is what you were looking for
anonymous
  • anonymous
oh. it is! ahaha thanks.
anonymous
  • anonymous
In general, \[ \cos A \cdot \cos 2A \cdot \cos 2^{2}A \cdot \cos 2^{3}A \cdots \cos 2^{n-1}A = \frac { \sin 2^n A}{ 2^n \sin A } \] \[ \implies 2^n \sin A \cdot \cos A \cdot \cos 2A \cdot \cos 2^{2}A \cdot \cos 2^{3}A \cdots \cos 2^{n-1}A= \sin 2^n A\]
TuringTest
  • TuringTest
nice^
anonymous
  • anonymous
Thanks :)

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