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May 3rd, 2009, 05:20 PM   #1
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Trigonometric identity

i need help with this, can anyone help please, tan? = 1 - cos2?/sin2? . \i've been stuck on this for a while, and i cannot figure it out, could someone show me how it is done. Thanks
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May 4th, 2009, 03:48 PM   #2
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Re: Trigonometric identity

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Originally Posted by munkiemunkie007
i need help with this, can anyone help please, tan? = 1 - cos2?/sin2? . \i've been stuck on this for a while, and i cannot figure it out, could someone show me how it is done. Thanks
Are you trying to solve an equation or prove an identity? It looks to me that it is not an identity.
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May 4th, 2009, 04:50 PM   #3
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Quote:
Originally Posted by munkiemunkie007
tan? = 1 - cos2?/sin2?
I think you meant tan? = (1 - cos2?)/sin2? (provided sin(2?) is not zero).
Standard identities tell you that cos(2?) = 1 - 2 sin? and sin(2?) = 2 sin(?)cos(?).
Hence (1 - cos(2?))/sin(2?) = 2 sin? / (2 sin(?)cos(?)) = sin(?)/cos(?) = tan(?).
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