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Trig limit

  1. Feb 6, 2007 #1
    lim x-> 7pi/4 (cosx+sinx)/(cos2x)

    so what i was trying to do here was replace cos2x with the double angle id which is cos^2x-sin^2x

    then i factor that and cancle out cosx+sinx

    now i have 1/cosx-sinx...so i tried direct sub. and i get 1/sqroot2/2+squroot2/2 which i end up with sqroot 2 but that isn't the right answer

    isn't cos 7(pi/4)= squroot 2/2 and sin 7(pi/4)= -squroot2/2?

    please show me where i am going wrong
  2. jcsd
  3. Feb 7, 2007 #2


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    Homework Helper

    You should end up with [itex] \frac{1}{\sqrt{2}}=\frac{\sqrt{2}}{2} [/itex].
  4. Feb 7, 2007 #3

    Gib Z

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    Homework Helper

    He means you did your algebra wrong btw.
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