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Help with this math Transformation

  1. Mar 7, 2007 #1
    Can anyone explain why (cos(x))^2 = (1+cos(2x))/2 ?
  2. jcsd
  3. Mar 7, 2007 #2
    cos(x)=(Exp(ix)+Exp(-ix))/2 right? do u know this formula?
    square before and after the '='
    then simplify it..
  4. Mar 7, 2007 #3


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    Staff Emeritus
    Science Advisor

    If you don't want to use complex numbers, remember that cos2x= cos2 x- sin2 x so that the right hand side is (1+ cos2 x- sin2x)/2. Do you see an "obvious" way to simplify 1+ cos2 x- sin2x?
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