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Basic algebra concept is puzzling me

  1. Dec 22, 2011 #1
    basic algebra concept is puzzling me....

    1. The problem statement, all variables and given/known data
    I don't understand why √10-5 + √5 = 2√5
    Could someone please explain this to me real quick...totaly forgot why this is :P


    2. Relevant equations
    none


    3. The attempt at a solution
    here I am! thoughts about it and I am still puzzled does it have anything to do with the fact that √10-5 =√5 and then we add another √5 to it and there is some rule that says that you take one of them away and just put a 2 infront of √5 and it is equivilant?
     
  2. jcsd
  3. Dec 22, 2011 #2

    Dick

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    Re: basic algebra concept is puzzling me....

    Yes. sqrt(5)+sqrt(5)=2*sqrt(5). Is that really something you forget? It's kind of the definition of multiplication.
     
  4. Dec 22, 2011 #3
    Re: basic algebra concept is puzzling me....

    its probobly just all the √ and stuff...it often scares me and I think automaticaly different rules apply or something....

    could someone explain limit equations with trig functions in them? I have no idea how to figure these out....for example:
    limit as x->0 for x/sin3x
     
    Last edited by a moderator: Dec 23, 2011
  5. Dec 22, 2011 #4

    Dick

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    Re: basic algebra concept is puzzling me....

    No, no different rules apply. For the second one, do you know limit as u->0 u/sin(u)=1? If so, put u=3x.
     
    Last edited by a moderator: Dec 23, 2011
  6. Dec 22, 2011 #5
    Re: basic algebra concept is puzzling me....

    so the answer would be 1/3 yes?
    now if it was instead sin 5x would it now be 1/5?
    thank you for help!
     
    Last edited by a moderator: Dec 23, 2011
  7. Dec 23, 2011 #6
    Re: basic algebra concept is puzzling me....


    TheKracken,

    you must use grouping symbols around this radicand, otherwise what
    you have is

    √(10) - 5 + √5 = 2√5, which is not what you meant.
     
  8. Dec 23, 2011 #7

    Dick

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    Re: basic algebra concept is puzzling me....

    You're welcome. Sure. The answer is 1/3.
     
    Last edited by a moderator: Dec 23, 2011
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