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Vectors and linear combinations

Addition and scalar multiplication drawn as arrows in the plane, and the equivalence between a linear combination and a consistent augmented system.

Understanding Linear Algebra, Vectors and linear combinations

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6 exercises

Activity 2.1.3

  1. Given the vectors , can b\bvec be expressed as a linear combination of v1\vvec_1, v2\vvec_2, and v3\vvec_3? Rephrase this question by writing a linear system for the weights c1c_1, c2c_2, and c3c_3 and use the Sage cell below to answer this question.

  2. Consider the following linear system. Identify vectors v1\vvec_1, v2\vvec_2, v3\vvec_3, and b\bvec such that the question "Is this linear system consistent?" is equivalent to the question "Can b\bvec be expressed as a linear…

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Exercise 3

Consider the vectors

  1. Find the linear combination with weights c1=2c_1 = 2, c2=−3c_2=-3, and c3=1c_3=1.

  2. Can you write the vector 0=[00]{\mathbf 0} = \left[\begin{array}{r} 0 \\ 0 \end{array}\right] as a linear combination of v1\vvec_1, v2\vvec_2, and v3\vvec_3? If so, describe all the ways in which you can do so.

  3. Can you write the vector 0=[00]{\mathbf 0} = \left[\begin{array}{r} 0 \\ 0 \end{array}\right] as a linear combination using just the first two vectors v1\vvec_1 v2\vvec_2? If so, describe all the ways in which you can do so.

  4. Can you write v3\vvec_3 as a linear combination of v1\vvec_1 and v2\vvec_2? If so, in how…

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Exercise 4

Nutritional information about a breakfast cereal is printed on the box. For instance, one serving of Frosted Flakes has 111 calories, 140 milligrams of sodium, and 1.2 grams of protein. We may represent this as a vector . One serving of Cocoa Puffs has 120 calories, 105 milligrams of sodium, and 1.0 grams of protein.

  1. Write the vector describing the nutritional content of Cocoa Puffs.

  2. Suppose you eat…

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Exercise 5

Consider the vectors

  1. Can you express the vector b=[101−8]\bvec=\left[\begin{array}{r} 10 \\ 1 \\ -8 \end{array}\right] as a linear combination of v1\vvec_1, v2\vvec_2, and v3\vvec_3? If so, describe all the ways in which you can do so.

  2. Can you express the vector b=[371]\bvec=\left[\begin{array}{r} 3 \\ 7 \\ 1 \end{array}\right] as a linear combination of v1\vvec_1, v2\vvec_2, and v3\vvec_3? If so, describe all the ways in which you can do so.

  3. Show that v3\vvec_3 can be written as a linear combination of v1\vvec_1 and v2\vvec_2.

  4. Explain why any linear combination of v1\vvec_1, v2\vvec_2, and v3\vvec_3, can be rewritten as a l…

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Exercise 6

Consider the vectors For what value(s) of kk, if any, can the vector [k−25]\left[\begin{array}{r} k \\ -2 \\ 5 \end{array}\right] be written as a linear combination of v1\vvec_1 and v2\vvec_2?

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Exercise 7

Determine whether the following statements are true or false and provide a justification for your response.

  1. Given two vectors v\vvec and w\wvec, the vector 2v2\vvec is a linear combination of v\vvec and w\wvec.

  2. Suppose v1,v2,…,vn\vvec_1,\vvec_2,\ldots,\vvec_n is a collection of mm-dimensional vectors and that the matrix [v1v2…vn]\left[\begin{array}{rrrr} \vvec_1 & \vvec_2 & \ldots & \vvec_n \end{array}\right] has a pivot position in every row. If b\bvec is any mm-dimensional vector, then b\bvec can be written as a linear combination of v1,v2,…,vn\vvec_1,\vvec_2,\ldots,\vvec_n.

  3. Suppose v1,v2,…,vn\vvec_1,\vvec_2,\ldots,\vvec_n is a collection…

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Adapted from Understanding Linear Algebra © 2023 David Austin. Licensed under CC BY 4.0. Source: Understanding Linear Algebra. Imported at revision 3e6dced.