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8.E: Exercises for Chapter 8

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Calculational Exercises

1. Let AC3×3 be given by

A=[10i010i01]

(a) Calculate det(A).
(b) Find det(A4).

2. (a) For each permutation πS3 , compute the number of inversions in π, and classify π as being either an even or an odd permutation.

(b) Use your result from Part (a) to construct a formula for the determinant of a 3×3 matrix.

3. (a) For each permutation πS4, compute the number of inversions in π, and classify π as being either an even or an odd permutation.

(b) Use your result from Part (a) to construct a formula for the determinant of a 4×4
matrix.

4. Solve for the variable x in the following expression:

det([x131x])=det([1032x613x5]).

5. Prove that the following determinant does not depend upon the value of θ:

det([sin(θ)cos(θ)0cos(θ)sin(θ)0sin(θ)cos(θ)sin(θ)+cos(θ)1])

6. Given scalars α,β,γF, prove that the following matrix is not invertible:

[sin2(α)sin2(β)sin2(γ)cos2(α)cos2(β)cos2(γ)111]

Hint: Compute the determinant.

Proof-Writing Exercises

1. Let a,b,c,d,e,fF be scalars, and suppose that A and B are the following matrices:

A=[ab0c] and B=[de0f]

Prove that AB=BA if and only if det([bacedf])=0.

2. Given a square matrix A, prove that A is invertible if and only if ATA is invertible.

3. Prove or give a counterexample: For any n1 and A,B(R)n×n, one has

det(A+B)=det(A)+det(B).

4. Prove or give a counterexample: For any rR,n1 and ARn×n, one has

det(rA)=rdet(A).


This page titled 8.E: Exercises for Chapter 8 is shared under a not declared license and was authored, remixed, and/or curated by Isaiah Lankham, Bruno Nachtergaele, & Anne Schilling.

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