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Common Trig Identity Derivations

  1. Aug 28, 2011 #1
    I'm looking for a source online that gives the step by step derivation of common trig identities, such as sin(2theta) = 2sin(theta)cos(theta), cos(2theta) = cos2(theta)-sin2(theta), sin2(theta) = (1 - cos(2theta))/2, ect. I did do 20 minuntes or so of searching online, nothing was exactly what I was hoping for. Is there a website explaining the derivations or should I fork out the $100 for a trig text? Thanks
     
  2. jcsd
  3. Aug 28, 2011 #2

    rock.freak667

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    Homework Helper

    The simplest way uses the these identities:

    cos(A+B)= cosAcosB - sinAsinB

    and sin(A+B) = sinAcosB + sinBcosA

    then put A=B. Proving the above identities might prove to be a bit more difficult.
     
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