1. Mar 7, 2007 #1

   kasse

   

   Can anyone explain why (cos(x))^2 = (1+cos(2x))/2 ?

    

   kasse, Mar 7, 2007
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3. Mar 7, 2007 #2

   ziad1985

   

   cos(x)=(Exp(ix)+Exp(-ix))/2 right? do u know this formula?
   square before and after the '='
   then simplify it..

    

   ziad1985, Mar 7, 2007
4. Mar 7, 2007 #3

   HallsofIvy

   

   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?

    

   HallsofIvy, Mar 7, 2007

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