Math Problem Statement

Let b = [h; -3; 2h - 5], u = [1; 0; 0], and v = [2; 1; 3]. For what value of h is b in the span of u and v?

Solution

To solve the problem, we need to determine the value of hh such that the vector b\mathbf{b} is in the span of the vectors u\mathbf{u} and v\mathbf{v}.

Given:

b=[h32h5],u=[100],v=[213]\mathbf{b} = \begin{bmatrix} h \\ -3 \\ 2h - 5 \end{bmatrix}, \quad \mathbf{u} = \begin{bmatrix} 1 \\ 0 \\ 0 \end{bmatrix}, \quad \mathbf{v} = \begin{bmatrix} 2 \\ 1 \\ 3 \end{bmatrix}

Problem:

The vector b\mathbf{b} is in the span of u\mathbf{u} and v\mathbf{v} if there exist scalars aa and bb such that: b=au+bv\mathbf{b} = a\mathbf{u} + b\mathbf{v} This expands to: [h32h5]=a[100]+b[213]\begin{bmatrix} h \\ -3 \\ 2h - 5 \end{bmatrix} = a\begin{bmatrix} 1 \\ 0 \\ 0 \end{bmatrix} + b\begin{bmatrix} 2 \\ 1 \\ 3 \end{bmatrix}

Expanding the equation:

[h32h5]=[a+2bb3b]\begin{bmatrix} h \\ -3 \\ 2h - 5 \end{bmatrix} = \begin{bmatrix} a + 2b \\ b \\ 3b \end{bmatrix}

This gives us the system of equations:

  1. h=a+2bh = a + 2b
  2. 3=b-3 = b
  3. 2h5=3b2h - 5 = 3b

Solve the system:

  1. From equation 22, we have b=3b = -3.

  2. Substitute b=3b = -3 into the third equation: 2h5=3(3)=92h - 5 = 3(-3) = -9 2h=9+5=42h = -9 + 5 = -4 h=2h = -2

  3. Finally, substitute h=2h = -2 and b=3b = -3 into the first equation: 2=a+2(3)-2 = a + 2(-3) 2=a6-2 = a - 6 a=4a = 4

Conclusion:

The value of hh that ensures b\mathbf{b} is in the span of u\mathbf{u} and v\mathbf{v} is 2\boxed{-2}.

This corresponds to option d).


Would you like more details or have any further questions? Here are some related questions you might find useful:

  1. What does it mean for a vector to be in the span of other vectors?
  2. How can you determine if a set of vectors are linearly independent?
  3. What is the geometric interpretation of the span of two vectors?
  4. Can you have more than one solution for the scalars in a span problem?
  5. How does the dimension of the vector space affect the span?

Tip: Always check if a vector can be expressed as a linear combination of other vectors by setting up a system of linear equations.

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Math Problem Analysis

Mathematical Concepts

Linear Algebra
Vector Spaces
Span
Linear Combination

Formulas

b = a*u + b*v
h = a + 2b
2h - 5 = 3b

Theorems

Linear Independence and Span

Suitable Grade Level

Undergraduate