Linear Algebra : Linear Equations

Study concepts, example questions & explanations for Linear Algebra

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Example Questions

Example Question #11 : Reduced Row Echelon Form And Row Operations

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Example Question #12 : Reduced Row Echelon Form And Row Operations

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Example Question #13 : Reduced Row Echelon Form And Row Operations

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Example Question #14 : Reduced Row Echelon Form And Row Operations

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Example Question #15 : Reduced Row Echelon Form And Row Operations

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Example Question #11 : Linear Equations

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Example Question #17 : Reduced Row Echelon Form And Row Operations

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Example Question #11 : Linear Equations

Give the elementary matrix that represents performing the row operation

in solving a three-by-three linear system.

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Correct answer:

Explanation:

The elementary matrix that represents a row operation is the result of performing the same operation on the appropriate identity matrix - which here is the three-by-three matrix . The row operation  is the multiplication of each element of in the second row of an augmented matrix by the scalar , so do this to the identity:

This is the correct response.

Example Question #19 : Reduced Row Echelon Form And Row Operations

Which of the following is an example of an elementary matrix?

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Correct answer:

Explanation:

An elementary matrix is one that can be formed from the (here, three-by-three) identity matrix

by way of exactly one row operation. An elementary matrix can have one of the following characteristics:

1) Exactly two rows are switched. The only choice that repositions rows is 

,

but this choice rearranges all three rows, so this is incorrect.

2) All of the "1" elements in the diagonal remain unchanged, but exactly one "0" is changed to a nonzero number. The choice that leaves all "1" elements unchanged is

but this matrix changes two of the zeroes to nonzero elements.

3) One of the "1" elements in the diagonal is changed to another nonzero element. The other three choices change these elements. But, of them:

changes two of the "1" elements to other nonzero numbers, and

also changes a "0" to a nonzero number.

,

however, makes one such change and no others, so it is an elementary matrix, and it is the correct choice.

Example Question #11 : Linear Equations

Which of the following elementary matrices represents the row operation

 

on a four-by-four system?

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None of the other choices gives the correct response.

Correct answer:

Explanation:

An elementary matrix is one that can be formed from the (here, four-by-four) identity matrix

by way of exactly one row operation.  represents the addition of  times each element in Row 1 to the corresponding element in Row 4, so do this in the identity matrix:

,

the correct choice.

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