Can Linear Independence of Vector Pairs Imply Independence of Their Union?

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In summary, the statement "if {v1,v3}, {v2,v3}, and {v1,v3} are all linearly independent, then{v1,v2,v3} is not linearly independent" is not necessarily true. In some cases, such as in a 1 or 2-dimensional vector space, it is trivially true that any set of 3 vectors is linearly dependent. However, in 3 or more dimensions, there can be sets of 3 independent vectors that are not necessarily linearly independent. The example given, where v1=1,v2=0, and v3=1, does not work because it includes the 0 vector, which automatically makes any set of
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physicsss
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prove if {v1,v3}, {v2,v3}, and {v1,v3} are all linearly independent, then{v1,v2,v3} is not linearly independent.

I'm having trouble showing that is true other than showing a counter example when it doesn't work, namely when v1=1,v2=0, and v3=1.

TIA.
 
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erm, what vector space are these vectors in? without that info the question is meaningless. actually, even iwth that info i think it is meanignless, or at least false or true for trivial reasons.
 
  • #3
Elaboration.

in any 1 or 2-d vector space three vectors are always linearly dependent and the conditions on the paris are neither here nor there. ie it is trivillay true.

in 3 or more dimensions then there are 3 dependent vectors that are pariwise linerly independent and there are 3 vector that are L.I. that are nec. pariwise independent so the theorem is false.
 
  • #4
physicsss said:
prove if {v1,v3}, {v2,v3}, and {v1,v3} are all linearly independent, then{v1,v2,v3} is not linearly independent.

I'm having trouble showing that is true other than showing a counter example when it doesn't work, namely when v1=1,v2=0, and v3=1.

TIA.
Do you mean not necessarily independent? As Matt Grime pointed out, if the dimension of the space is less than 3, it is true that no set of 3 vectors is independent- the condition that any pair are independent is irrelevant while if the dimension is three or greater, this is not necessarily true. In three or more dimensions it is the case that if a set of 3 vectors is independent, then any pair are independent.
If the point was to show that {v1, v2, v3} is not necessarily independent, then an example would be sufficient. However, the example you cite does not work since {v1, v2} and {v2, v3} are not independent- any set of vectors that includes the 0 vector cannot be independent.
 

FAQ: Can Linear Independence of Vector Pairs Imply Independence of Their Union?

What is the difference between independent and dependent variables?

Independent variables are variables that are manipulated or controlled by the researcher, while dependent variables are the outcome or result of the manipulation of the independent variable.

How do you determine whether a variable is independent or dependent?

The best way to determine whether a variable is independent or dependent is to ask yourself: "Is this variable being manipulated or controlled by the researcher?" If the answer is yes, then it is an independent variable. If the answer is no, then it is a dependent variable.

Can a variable be both independent and dependent?

No, a variable cannot be both independent and dependent at the same time. However, a variable can be independent in one study and dependent in another study, depending on how it is being manipulated.

What is the purpose of distinguishing between independent and dependent variables?

Distinguishing between independent and dependent variables is important because it helps to establish cause and effect relationships in research. By manipulating the independent variable and observing the changes in the dependent variable, researchers can determine whether the independent variable has a direct impact on the dependent variable.

How do you control for confounding variables in a study?

Confounding variables are variables that can affect the relationship between the independent and dependent variables. To control for confounding variables, researchers must carefully design their study and use techniques such as randomization, control groups, and statistical analysis to minimize their impact on the results.

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