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Solve cosxcos(-x) - sinxsin(-x) = 1

  1. Dec 8, 2007 #1
    cosxcos(-x) - sinxsin(-x) = 1

    I know I'm making it harder than it is, but I can't seem to figure it out.
    Any help would be appreciated.

    RaveN
     
  2. jcsd
  3. Dec 8, 2007 #2

    Dick

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    cos(-x)=cos(x). sin(-x)=-sin(x).
     
  4. Dec 8, 2007 #3
    When I plugged those in then I get cosx2 - sinx2 = 1 and then I get completely lost.
     
  5. Dec 8, 2007 #4

    Dick

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    When I plug them in I get cos(x)^2+sin(x)^2=1. There are two minus signs associated with the sin(x)^2.
     
  6. Dec 8, 2007 #5
    Because it's -sin to begin with. I knew I was making it too hard. Thanks.
     
  7. Dec 8, 2007 #6

    Hurkyl

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    Another way: isn't the l.h.s. in the form of an angle addition formula?
     
  8. Dec 8, 2007 #7

    HallsofIvy

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    Not with the correct signs! It's cos2(x)+ sin2(x)!
     
  9. Dec 8, 2007 #8

    Dick

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    It is cos(x+(-x)). That is another way to do it.
     
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