Answered

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Consider the matrix [tex]A_{4x4}, det(A) = -2[/tex]

Show that the following is true or false:


[tex]det(adj(2A^{-1}) =-2^{9}[/tex]

Sagot :

facundo3141592

We found a counterexample, so the statement is false.

Is the statement true?

Let's use the matrix:

[tex]\left[\begin{array}{cccc}-2&0&0&0\\0&1&0&0\\0&0&1&0\\ 0&0&0&1 \end{array}\right][/tex]

This is a 4x4 matrix with determinant equal to -2.

The inverse matrix is:

[tex]\left[\begin{array}{cccc}1/2&0&0&0\\0&-1&0&0\\0&0&-1&0\\ 0&0&0&-1 \end{array}\right][/tex]

If we multiply it by 2, we get:

[tex]\left[\begin{array}{cccc}1&0&0&0\\0&-2&0&0\\0&0&-2&0\\ 0&0&0&-2 \end{array}\right][/tex]

The adjoint of that is the original matrix, actually:

[tex]\left[\begin{array}{cccc}-2&0&0&0\\0&1&0&0\\0&0&1&0\\ 0&0&0&1 \end{array}\right][/tex]

Which we already know, has a determinant of -2.

So the statement is false, as we found a counterexample.

If you want to learn more about matrices:

https://brainly.com/question/11989522

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