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Homework Help: Cosine Law Query?

  1. Nov 29, 2013 #1
    My online physics course is using cosine law to find the net forces on objects. My question is to do with the equation, at first it shows it as : c^2=a^2+b^2-2ab cosC.

    From there, it changes to: c=[a^2+b^2-2ab cosC]^1/2.

    How and why does this work? Why isn't a square root involved in the operation?
  2. jcsd
  3. Nov 29, 2013 #2
    The notation ##x^{1/2}## is just another notation for ##\sqrt{x}##. Was that your question?
  4. Nov 29, 2013 #3
    Yes, thank you! I see now, it seemed like I was getting the wrong answer when I was doing the original equation, so I thought something else was at play here.

    Is there any reason why one would prefer writing the equation this way? I just don't get why my textbook would switch the equation when trying ton present new information.
  5. Nov 29, 2013 #4


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    hi paolostinz! :smile:
    you mean, writing c instead of c2 ?

    or writing (…)1/2 instead of √(…) ?

    we usually want c itself, so the fact that it comes from an equation with c2 is a nuisance

    (…)n is the general way of writing powers: there's no really good reason for having a special symbol when n = 1/2, and the bar of √, which should really go over the top of the bracket, is a nuisance when the bracket is long :wink:
  6. Nov 29, 2013 #5
    See, that makes sense, it's the little things like this that confuse me most. I wish I had better access to teachers to clear up these type of hiccups. I'm so grateful for this place, thank you everyone!
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