06.09.2021 Views

Linear Algebra, Theory And Applications, 2012a

Linear Algebra, Theory And Applications, 2012a

Linear Algebra, Theory And Applications, 2012a

SHOW MORE
SHOW LESS

Create successful ePaper yourself

Turn your PDF publications into a flip-book with our unique Google optimized e-Paper software.

7.3. EXERCISES 169<br />

22. Find the complex eigenvalues and eigenvectors of the matrix<br />

Determine whether the matrix is defective.<br />

23. Find the complex eigenvalues and eigenvectors of the matrix<br />

Determine whether the matrix is defective.<br />

⎛<br />

24. Find the complex eigenvalues and eigenvectors of the matrix<br />

⎞<br />

⎠ . Determine<br />

whether the matrix is defective.<br />

25. Here is a matrix. ⎛<br />

⎜<br />

⎝<br />

1 a 0 0<br />

0 1 b 0<br />

0 0 2 c<br />

0 0 0 2<br />

⎞<br />

⎟<br />

⎠<br />

⎛<br />

⎝<br />

−4 2 0<br />

2 −4 0<br />

−2 2 −2<br />

⎞<br />

⎠ .<br />

⎛<br />

⎞<br />

7 −5 −6 ⎠ .<br />

⎝ 1 1 −6<br />

−1 7 2<br />

⎝ −2 4 0<br />

4 2 0<br />

−2 2 6<br />

Find values of a, b, c for which the matrix is defective and values of a, b, c for which it<br />

is nondefective.<br />

26. Here is a matrix. ⎛<br />

⎝<br />

a 1 0<br />

0 b 1<br />

0 0 c<br />

where a, b, c are numbers. Show this is sometimes defective depending on the choice<br />

of a, b, c. What is an easy case which will ensure it is not defective?<br />

27. Suppose A is an n × n matrix consisting entirely of real entries but a + ib is a complex<br />

eigenvalue having the eigenvector, x + iy. Here x and y are real vectors. Show that<br />

then a − ib is also an eigenvalue with the eigenvector, x − iy. Hint: You should<br />

remember that the conjugate of a product of complex numbers equals the product of<br />

the conjugates. Here a + ib is a complex number whose conjugate equals a − ib.<br />

28. Recall an n × n matrix is said to be symmetric if it has all real entries and if A = A T .<br />

Show the eigenvalues of a real symmetric matrix are real and for each eigenvalue, it<br />

has a real eigenvector.<br />

29. Recall an n × n matrix is said to be skew symmetric if it has all real entries and if<br />

A = −A T . Show that any nonzero eigenvalues must be of the form ib where i 2 = −1.<br />

In words, the eigenvalues are either 0 or pure imaginary.<br />

30. Is it possible for a nonzero matrix to have only 0 as an eigenvalue?<br />

31. Show that the eigenvalues and eigenvectors of a real matrix occur in conjugate pairs.<br />

32. Suppose A is an n × n matrix having all real eigenvalues which are distinct. Show<br />

there exists S such that S −1 AS = D, a diagonal matrix. If<br />

⎛<br />

⎞<br />

λ 1 0<br />

⎜<br />

D = ⎝<br />

. ..<br />

⎟<br />

⎠<br />

0 λ n<br />

⎞<br />

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!