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How to tell if a pair of functions are linearly dependent or linearly independent |
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| Mar5-12, 06:32 PM | #1 |
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How to tell if a pair of functions are linearly dependent or linearly independent
1. The problem statement, all variables and given/known data
Determine if the pair of functions given are linearly independent or linearly dependent on the interval 1<x<∞, and give a reason for your answer. y1=|x| y2=-3x 2. Relevant equations I'm pretty sure this has something to do with the Wronskian. W(f,g)=fg'-f'g 3. The attempt at a solution f=y1, g=y2 f'=1, g'=-3 I can assume that the derivative of the abs. value of x is just 1, because the question says that x is greater than 1, right? So then W(f,g)=-3|x|+3x can i assume x is positive again, so therefore the Wronskian is equal to zero? Would this then make my solution linearly independent? Thanks. |
| Mar5-12, 06:37 PM | #2 |
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Maybe I'm misunderstanding the question, but it seems to me that all you have to do is see whether they are linear combinations of each other. does y1(x) = a*y2(x) for all x in the domain, for some constant a?
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| Mar5-12, 07:41 PM | #3 |
Recognitions:
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Technically just showing that the Wronskian is zero doesn't tell you the functions are linearly dependent. There are exceptions to that. Follow the suggestion 80past2 gave.
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