Trig Identities

  • Thread starter cscott
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Main Question or Discussion Point

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]?
 

Answers and Replies

786
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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.
 
TD
Homework Helper
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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]
 
783
1
Damn, I guess I wasn't looking at them right. Thanks.
 
Hurkyl
Staff Emeritus
Science Advisor
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You don't need trig identities to differentiate those...
 

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