Express as a linear combination

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SUMMARY

The vectors v1 = [1, -3], v2 = [2, -8], and v3 = [-3, 7] span R² but do not form a basis due to linear dependence, specifically v3 = v1 + v2. To express the vector [1, 1] as a linear combination, two valid representations are 5v1 - 2v2 = [1, 1] and 10v1 - 3v2 + v3 = [1, 1]. The first representation arises from solving the system with v1 and v2, while the second incorporates the linearly dependent vector v3, leading to an infinite number of solutions.

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Homework Statement


The vectors v1= [1, -3], v2= [2, -8], v3= [ -3, 7] span R2 but do not form a basis. Find 2 different ways to express [1, 1] as a linear combination of v1, v2, v3.




The Attempt at a Solution



Since it states that the set is not a basis, then v3=v1+v2. I solved the system v1+v2=[1,1] and got 5v1-2v2=[1,1]. The second answer the book gives is 10v1-3v2+v3. How did they get the second answer?
 
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If you solve c1*v1+c2*v2=[1,1] you get a unique solution since [v1,v2] are a basis. To get the second answer you solve c1*v1+c2*v2+c3*v3=[1,1]. Since [v1,v2,v3] are linearly dependent, and hence are not a basis, you get an infinite number of solutions. The books answer is only one of them.
 

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