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Trig Identities

  1. Aug 24, 2005 #1
    How can I use trig identities to let me differentiate [itex]\sin \left ( x + \frac{\pi}{2} \right)[/itex] and [itex]3 \sin x - 2 \cos x[/itex]?
     
  2. jcsd
  3. Aug 24, 2005 #2
    Well, there's an identity for [tex]\sin{(\alpha+\beta)}[/tex] but why would you want to use it? Those can be differentiated easily... I'm missing something.
     
  4. Aug 24, 2005 #3

    TD

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    Well, [itex]\sin \left ( x + \frac{\pi}{2} \right) = \cos x[/itex] if that helps :smile:

    I don't see why you'd want to change the second one though, taking the derivative is lineair so [itex]\left( {3\sin x - 2\cos x} \right)^\prime = 3\left( {\sin x} \right)^\prime - 2\left( {\cos x} \right)^\prime [/itex]
     
  5. Aug 24, 2005 #4
    Damn, I guess I wasn't looking at them right. Thanks.
     
  6. Aug 24, 2005 #5

    Hurkyl

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    You don't need trig identities to differentiate those...
     
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