3.4: Applications of the Determinant
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Cramer’s Rule
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Determine if a Matrix is Invertible (nonsingular) Using a Determinant
Let .
Determinant of matrix
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Matrix has a determinant of 0, so it is singular and not invertible.
Solution
Write the matrix :
Compute the determinant of by expanding along the first row:
Compute the determinants:
For the first minor:
The second term is multiplied by , so it is .
For the third minor:
Substitute these results back into the expansion:
Since , the matrix is singular (noninvertible).
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The Deep Dive
To find the determinant of the matrix , which is a matrix, you can use the formula involving minors and cofactors. Specifically, the determinant can be calculated by expanding it along the first row:
Calculating the minor determinants, we actually find that the determinant of is .
Interestingly, if a matrix has a determinant of zero, it implies that the matrix is singular, meaning it does not have an inverse. This can spur on interesting situations in linear algebra, especially when solving systems of equations where you might end up with dependent equations!
When applying determinants in real-world problems, you’ll find they can be crucial in fields such as physics and computer graphics. For example, calculating areas and volumes in multi-dimensional space often involves determinants. In graphics, they help determine transformations and affect object orientations, making sure things don’t get upside down or inside out!