Question Details

If A =  then det(A-1) is _____________ (correct to two decimal places).

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Correct Answer :

0.25

Solution :

The correct answer is 0.25.

To find the determinant of the inverse matrix, we use the property of determinants for invertible matrices, which states that:
det(A-1)=1det(A)

From the given image, the matrix A is:
A=[123045001]

Notice that matrix A is an upper triangular matrix (all entries below the main diagonal are zero). The determinant of any triangular matrix is simply the product of its diagonal elements:
det(A)=1×4×1=4

Alternatively, we can compute the determinant by expanding along the first column:
det(A)=1×(4×1-5×0)-0+0=4

Now, using the relationship between the determinant of a matrix and its inverse:
det(A-1)=14=0.25

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