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    The union of three subspaces of V is a subspace of V

    I know, this is only one case of three other cases. I'm trying to prove, exhaustively, that for the union of three subspaces to be a subspace one of them must contain both of them. The first case I consider is if this condition (x ∈ Ua and y ∈ Ub then x+y belongs to either one of them, as...
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    The union of three subspaces of V is a subspace of V

    Yeah, I apologize for the mess. I found it very difficult to organize my thoughts regarding this question and I ended up writing it in an unclear way. What I'm trying to prove is this: (Union of three subspaces of V is a subspace of V) ##\Rightarrow## (One of the subspaces contains the other...
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    The union of three subspaces of V is a subspace of V

    Homework Statement This is the exact phrasing form Linear Algebra Done Right by Axler: Prove that the union of three subspaces of V is a subspace of V if and only if one of the subspaces contains the other two. [This exercise is surprisingly harder than the previous exercise, possibly because...
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    Chemistry questions

    I'm taking a course in chemistry and I need some help, I have some questions : 1.Why do ions, strong acids,bases etc. conduct electricity well ? 2.In the periodic table, are the masses of atoms in amu or grams? what's the difference? and why is Carbon 14 the standard ? why do we need a...
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    Help in The Oxidation Number Method ?

    Ok here is the original equation : Cu+HNO3 = Cu(NO3)2+NO2+H2O Now according to "The Oxidation Number Method", I must balance the charges first and if you look at the equation you will find that : Cu -> lost 2electrons N -> gained 1electron Then balance the charges by multiplying N by 2, so I...
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    Help in The Oxidation Number Method ?

    Help in "The Oxidation Number Method"? Homework Statement I just learned how to balance the redox reactions with this method, but there is something I don't understand ... Look at this example : Cu+HNO3 = Cu(NO3)2+NO2+H2O after making the number of electrons gained and lost equal we get...
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    Questions about evolution

    Hey guys I was in a discussion with my friend and I couldn't answers some questions about evolution .. and since I'm not that good in biology, I hope that I get some explained answers. Q1 : How can mutations produce organs ? Q2 : Do genetic mutations produce positive and negative changes ...
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    How can I find the net force of this ? (image included)

    It's just an example for me to understand something, but I didn't know that it missed some additional info sorry, lol. Let's suppose that the angle is 45 degree.
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    How can I find the net force of this ? (image included)

    Both arrows have the same angles http://imageshack.us/photo/my-images/337/drawingz.png/ How can I find the net force of this and the direction ? Thanks.
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    Need explanation on how electrons and electricity work

    Hey guys I'm a new member and I will be mostly asking questions :P Anyways ... Physics subjects in my school are about electricity now and my teachers aren't very good, so I can't clearly understand what they're saying. To get to the bottom line, our lesson was about electrons and...
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