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Homework Help: Limit question. Have solution, need to know how to get it.

  1. Dec 5, 2012 #1
    1. The problem statement, all variables and given/known data

    I was working on a problem in my book, and I didn't know how to answer the question. So I looked at the solution manual. and it had this


    I do not know where the (cosx + 1) on the bottom came from. Any ideas? Please explain.

    2. Relevant equations

    sin(x+y)= sinx cosy + cosx siny

    3. The attempt at a solution

    I get the top part though, you factor out the 2, multiply the cos and sin then it becomes sin(x+y) sorta thing.

    Ok, nevermind, I am sorry, I didn't realise they factored out the cosx-1 and then multiplied by (cosx +1)/(cosx+1) So I got it now.
  2. jcsd
  3. Dec 5, 2012 #2


    Staff: Mentor

    They multiplied by 1 in the form
    $$ \frac{cos(x) + 1}{cos(x) + 1}$$
    One that is relevant to the question you asked is:
    sin2(x) + cos2(x) = 1
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