Linear Algebra II Tutorial Sheet no. 2
Summer term 2011
Prof. Dr. Otto April 18, 2011
Dr. Le Roux Dr. Linshaw
Exercise T1 (Geometric characterisation of linear maps by eigenvalues)
Give a geometric description of all the endomorphisms ofR3with the following sets of eigenvalues:
(a) λ1=−1,λ2=0,λ3=1 (b) λ1=1,λ2=2,λ3=3
(c) λ1=−1,λ2=1,λ3=2
Note that you cannot assume anything about the corresponding eigenvectors other than that they form a basis (why?).
Exercise T2 (Eigenvalues and eigenvectors overRandC) LetAbe the3×3-matrix
0 −1 4
1 0 2
0 0 1
.
(a) Determine the characteristic polynomial of the matrixA.
(b) Find all real eigenvalues ofAand the corresponding eigenvectors of the mapϕ:R3→R3withϕ(x) =Ax.
(c) Find all eigenvalues for the corresponding mapϕ:C3→C3withϕ(x) =Axand give a basis of each eigenspace.
Exercise T3 (Diagonalisation) Consider the matrixA=
2 2 1 3
overR.
(a) Determine all eigenvalues ofAand corresponding eigenvectors.
(b) Find a regular matrixCsuch thatD=C−1ACis a diagonal matrix.
(c) CalculateA6.
(d) Find a “positive square root” ofA, i.e., find a matrixRwith non-negative eigenvalues such thatR2=A (e) Check thatt7→etAv0solves the differential equation d tdv(t) =Av(t)with initial valuev(0) =v0. Exercise T4 (Eigenvalues of nilpotent maps)
Let V be a vector space of dimension greater than 0, and letϕ :V → V be a nilpotent endomorphism, that is, an endomorphism such thatϕk=0for somek∈N.
(a) Show that 0 is the only possible eigenvalue ofϕ.
(b) Show that 0 is an eigenvalue ofϕ.
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