hw12.5. find the basis for an eigenspace using spectral theorem suppose that a real, symmetric matrix has two distinct eigenvalues and . if are an eigenbasis for the -eigenspace, find an orthonormal basis for the -eigenspace. you may use a scientific calculator. basis



Answer :

An orthonormal basis for the -eigenspace of [tex]\pi[/tex]2 is

B1=(V3=[tex]\left[\begin{array}{ccc}1/\sqrt{3}\\1\sqrt{3}\\1/\sqrt{3} \end{array}\right][/tex]

What is Spectral Theorem?

There exists an invertible matrix C such that C 1 M C C-1 MC C1MC is a diagonal matrix, according to the spectral theorem, which asserts that if M equals the transpose of M, then M is diagonalizable.

Concept of theorem

If A is a symmetric matrix, then eigenvectors of different eigenvalues are orthogonal

here if v3 is an eigenvectors for eigenvalues [tex]\pi[/tex]2 of matrix A,then by spectral theorem we have

v1.v3=0

-2x+0y+2z=0 ------------(1)

and v2.v3=0

-2x+y+z=0 ------------(2)

To find v3 we have solve system

-2x+0y+2z=0

-2x+y+z=0

[tex]\left[\begin{array}{ccc}-2&0&-1\\-2&1&1\end{array}\right][/tex] [tex]\left[\begin{array}{ccc}x\\y\\z\end{array}\right][/tex] = [tex]\left[\begin{array}{ccc}0\\0\\\end{array}\right][/tex]

Applying R1 = -1/2 X R1

               R2= R2+2 X R2 We get

[tex]\left[\begin{array}{ccc}1&0&-1\\0&1&-1\\\end{array}\right][/tex][tex]\left[\begin{array}{ccc}x\\y\\z\end{array}\right][/tex] = [tex]\left[\begin{array}{ccc}0\\0\\\end{array}\right][/tex]

x-z=0

y-z=0

put z=t

x=t

y=t

[tex]\left[\begin{array}{ccc}x\\y\\z\end{array}\right][/tex]=[tex]\left[\begin{array}{ccc}t\\t\\t\end{array}\right][/tex]=t[tex]\left[\begin{array}{ccc}1\\1\\1\end{array}\right][/tex]

thus eigenvector for eigenvalue [tex]\pi[/tex]2 is v3=[tex]\left[\begin{array}{ccc}1\\1\\1\end{array}\right][/tex]

and basis for eigenspace of [tex]\pi \\[/tex]2 is B=[tex]\left[\begin{array}{ccc}1\\1\\1\end{array}\right][/tex]

Next we will convert v3 into a unit vector

for this v3=[tex]\sqrt{(1.1)+(1.1)+(1.1)}[/tex] = [tex]\sqrt{v3.v3}[/tex]

v3=[tex]\sqrt{3}[/tex]

v3= v3/v3 =1/[tex]\sqrt{3}[/tex] (1   1   1)

an orthonormal basis for the -eigenspace is B1 = V3=[tex]\left[\begin{array}{ccc}1/\sqrt{3} \\1/\sqrt{3} \\1/\sqrt{3} \end{array}\right][/tex]

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