in Linear Algebra edited by
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8 votes
8 votes
You have a matrix $A$ with the factorization:
$$
A=\underbrace{\left(\begin{array}{ccc}
1 & & \\
3 & 2 & \\
1 & -1 & 2
\end{array}\right)}_B \quad \underbrace{\left(\begin{array}{ccc}
1 & 3 & 1 \\
2 & -1 \\
& 2
\end{array}\right)}_{C=B^T} .
$$
The Entries which are not shown in factorization are zeros.

What is the product of the $3$ eigenvalues of $A?$
in Linear Algebra edited by
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2 Comments

The Matrix C Doesn't seem Transpose of Matrix B. The Elements of matrix Dont Match.
0
0
The Transpose will be  1   3    1

                                      0    2    -1

                                       0    0      2
3
3

1 Answer

11 votes
11 votes
The product of the eigenvalues is $\operatorname{det} A=\operatorname{det} B \times \operatorname{det} C$. $B$ and $C$ are triangular matrices so their determinants are just the products of their diagonals $=1 \times 2 \times 2=4$, hence $\operatorname{det} A=4^2=16$.

1 comment

Sir, I did understand the problem and the concept that was applied here.....But what i did not understand was that why is the matrix C given in that manner...

I mean matrix C is the resultant of transpose of B. But the principle diagonal is shown to be different...?

Is it just a distraction for the actual question?
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0
Answer:

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