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Homework Help: Verifing trig identities

  1. Apr 3, 2010 #1

    I have to verify this identity and cant seem to figure it out. cos (x-y)=cos x * cos y + sin x * sin y
    well since cos y = 0, it kind of eliminates that side of the equation and I end up with sinx * sin1
    Did I go about this all wrong?
  2. jcsd
  3. Apr 3, 2010 #2


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    Homework Helper

    It is sin(x)*1 not sin 1, because sin(pi/2)=1. So far you have cos(x-pi/2)=sin(x), which is correct. Now write out the right hand side of your original equation and see what you get.
    Last edited: Apr 3, 2010
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