Linear Independence: V1-V4 in R4 - True or False?

In summary, the conversation discusses whether the statement "If V1...V4 are linearly independent vectors in R4, then {V1, V2, V3} are also linearly independent" is true or false. The attempt at a solution involves reducing the problem to 3 vectors in R3 and finding a counter example. The conversation also discusses the implications of assuming that {V1, V2, V3} are linearly dependent and how it would affect the equations. Ultimately, it is concluded that the statement is false if there exist non-zero values for c1, c2, c3, and c4 that satisfy the equation c1V1+c2V2+c3V3+c4V4
  • #1
thrive
19
0

Homework Statement



If V1...V4 are linearly independent vectors in R4, then {V1, V2, V3} are also linearly independent. True or False.



The Attempt at a Solution


My solution involved reducing the problem down the 3 vectors in R3. Then show a counter example of this in R3 although I have not been able to come up with one.
 
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  • #2
Why not assume that [itex]\{V_1,V_2,V_3\}[/itex] are linearly dependent, what would that mean?
 
  • #3
it would mean that the answer is false...
 
  • #4
Obviously, but that doesn't prove anything.

Start by assuming [itex]\{V_1,V_2,V_3\}[/itex] are linearly dependent, under that assumption, what could you say about the equation [itex]c_1V_1+c_2V_2+c_3V_3=0[/itex]?

What would that imply about the equation [itex]c_1V_1+c_2V_2+c_3V_3+c_4V_4=0[/itex]?
 
  • #5
it would mean there is some linear combination of c1, c2, c3 (not all zero) that would solve that first equation. In the second equation it would imply that not necessarily would there be a c4 to cancel the V4 term?
 
  • #6
thrive said:
it would mean there is some linear combination of c1, c2, c3 (not all zero) that would solve that first equation.

Right. So choose those values of c1, c2, and c3 and plug them into the second equation.

In the second equation it would imply that not necessarily would there be a c4 to cancel the V4 term?

If [itex]c_1V_1+c_2V_2+c_3V_3=0[/itex] then, [itex]c_4=0[/itex] would surely satisfy the equation [itex]c_1V_1+c_2V_2+c_3V_3+c_4V_4=0[/itex] right?

But if [itex]\{V_1,V_2,V_3\}[/itex] are linearly dependent, then there would exist [itex]c_1[/itex], [itex]c_2[/itex] and [itex]c_3[/itex] not all equal to zero, so even if [itex]c_4=0[/itex] there would exist [itex]c_1[/itex], [itex]c_2[/itex], [itex]c_3[/itex] and [itex]c_4[/itex] not all equal to zero that would make [itex]c_1V_1+c_2V_2+c_3V_3+c_4V_4=0[/itex], which would mean what?
 
  • #7
which would mean that the answer to the question is false
 
  • #8
No, if there exist [itex]c_1[/itex], [itex]c_2[/itex], [itex]c_3[/itex] and [itex]c_4[/itex] not all equal to zero that would make [itex]c_1V_1+c_2V_2+c_3V_3+c_4V_4=0[/itex], would the set [itex]\{V_1,V_2,V_3,V_4\}[/itex] be linearly independent or dependent?
 

Related to Linear Independence: V1-V4 in R4 - True or False?

1. What is linear independence?

Linear independence refers to a set of vectors in a vector space that cannot be written as a linear combination of each other. In other words, none of the vectors can be expressed as a scalar multiple of another vector in the set.

2. How can you determine if V1-V4 in R4 are linearly independent?

To determine if V1-V4 in R4 are linearly independent, you can use the row reduction method to create an augmented matrix and then check if the matrix has a unique solution. If there is a unique solution, then the vectors are linearly independent. If the matrix has no solution or infinitely many solutions, then the vectors are linearly dependent.

3. Can a set of vectors be linearly independent in one vector space but dependent in another?

Yes, a set of vectors can be linearly independent in one vector space but dependent in another. This is because the definition of linear independence is based on the vector space itself, and different vector spaces can have different dimensions and bases.

4. Is the statement "V1-V4 in R4 are linearly independent" always true?

No, the statement "V1-V4 in R4 are linearly independent" is not always true. It depends on the specific values of V1-V4 and the dimension of R4. For example, if V1 = [1, 0, 0, 0], V2 = [0, 1, 0, 0], V3 = [0, 0, 1, 0], and V4 = [0, 0, 0, 1], then the statement would be true. However, if any of the vectors were a linear combination of the others, the statement would be false.

5. How is linear independence related to the concept of a basis?

Linear independence is closely related to the concept of a basis. A basis for a vector space is a set of linearly independent vectors that span the entire space. This means that any vector in the space can be written as a linear combination of the basis vectors. In other words, the basis vectors form a coordinate system for the vector space. If a set of vectors is linearly dependent, it cannot form a basis for the space.

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