Math Problem Statement

Consider a matrix A:R^(3)->R^(2). Let {v_(1),v_(2),v_(3)} be a basis for R^(3) so that {Av_(1),Av_(2)} is a linearly independent set in R^(2). Question: Does A(x)=(0) have zero, one, or infinitely many solutions? Why?

Solution

Given that A:R3R2A: \mathbb{R}^3 \to \mathbb{R}^2 and we have the basis vectors {v1,v2,v3}\{v_1, v_2, v_3\} for R3\mathbb{R}^3, with the set {Av1,Av2}\{A v_1, A v_2\} being linearly independent in R2\mathbb{R}^2, the question asks about the number of solutions to the equation A(x)=0A(x) = 0, where xR3x \in \mathbb{R}^3.

Step-by-Step Analysis:

  1. Linear Transformation Properties:

    • AA is a linear transformation from a 3-dimensional space ( R3\mathbb{R}^3 ) to a 2-dimensional space ( R2\mathbb{R}^2 ).
    • The matrix representing AA must have dimensions 2×32 \times 3, since it's mapping from R3\mathbb{R}^3 to R2\mathbb{R}^2.
  2. Rank of the Matrix AA:

    • We are given that {Av1,Av2}\{A v_1, A v_2\} is a linearly independent set in R2\mathbb{R}^2. This implies that the image of AA contains at least two linearly independent vectors in R2\mathbb{R}^2.
    • Therefore, the rank of AA, which corresponds to the number of linearly independent columns, is at least 2.
    • Since AA is a 2×32 \times 3 matrix, the maximum possible rank of AA is 2 (because the number of rows in AA is 2).
  3. Dimension of the Kernel (Null Space):

    • By the rank-nullity theorem, we have: dim(Ker(A))+dim(Im(A))=3\text{dim}(\text{Ker}(A)) + \text{dim}(\text{Im}(A)) = 3
    • The rank of AA is 2, so: dim(Ker(A))+2=3\text{dim}(\text{Ker}(A)) + 2 = 3 dim(Ker(A))=1\text{dim}(\text{Ker}(A)) = 1
  4. Conclusion:

    • The dimension of the kernel (null space) of AA is 1. This means that the null space of AA is a 1-dimensional subspace of R3\mathbb{R}^3, implying there is a nontrivial solution to A(x)=0A(x) = 0.
    • Since the null space is 1-dimensional, there are infinitely many solutions to the equation A(x)=0A(x) = 0, because every scalar multiple of a nonzero vector in the kernel is also a solution.

Final Answer:

The equation A(x)=0A(x) = 0 has infinitely many solutions, as the null space of AA has dimension 1, meaning there is a 1-dimensional space of solutions.

Would you like further details on the rank-nullity theorem or kernel and image concepts?

Here are 5 related questions for deeper understanding:

  1. How does the rank-nullity theorem apply to transformations between spaces of different dimensions?
  2. What are the implications of a transformation having a rank less than the number of columns?
  3. Can the kernel of a matrix ever be trivial (just the zero vector)?
  4. How do the concepts of linear independence and rank relate to each other?
  5. What conditions must hold for a transformation to be injective?

Tip: When analyzing transformations, always check the dimensions of both the domain and codomain to predict the behavior of solutions, especially in solving equations like A(x)=0A(x) = 0.

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Math Problem Analysis

Mathematical Concepts

Linear Algebra
Linear Transformations
Kernel and Image
Rank-Nullity Theorem

Formulas

Rank-nullity theorem: dim(Ker(A)) + dim(Im(A)) = dim(domain(A))
Linear transformation equation: A(x) = 0

Theorems

Rank-Nullity Theorem

Suitable Grade Level

Undergraduate (1st-2nd year)