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Let d in R, and A[{:(,-2,4+d,(sin theta-...

Let `d in R, and A[{:(,-2,4+d,(sin theta-2)),(,1,(sin theta)+2,d),(,5,(2sin theta)d,(-sin theta)+2+2d):}]=theta in [0,2pi]` If the minimum value of det(A) is B. Then the value of d is:

A

`-5`

B

`2(sqrt2+2)`

C

`2(sqrt2+1)`

D

`-7`

Text Solution

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The correct Answer is:
To solve the problem, we need to find the value of \( d \) such that the minimum value of the determinant of matrix \( A \) is 8. We will follow these steps: ### Step 1: Write down the matrix \( A \) Given the matrix \( A \): \[ A = \begin{pmatrix} -2 & 4 + d & \sin \theta - 2 \\ 1 & \sin \theta + 2 & d \\ 5 & 2 \sin \theta d & -\sin \theta + 2 + 2d \end{pmatrix} \] ### Step 2: Calculate the determinant of \( A \) We will calculate the determinant \( \det(A) \) using the formula for the determinant of a 3x3 matrix: \[ \det(A) = a(ei - fh) - b(di - fg) + c(dh - eg) \] where \( a, b, c, d, e, f, g, h, i \) are the elements of the matrix \( A \). Substituting the values from matrix \( A \): \[ \det(A) = -2 \left( (\sin \theta + 2)(-\sin \theta + 2 + 2d) - d(2 \sin \theta d) \right) - (4 + d) \left( 1(-\sin \theta + 2 + 2d) - d(5) \right) + (\sin \theta - 2) \left( 1(2 \sin \theta d) - (\sin \theta + 2)(5) \right) \] ### Step 3: Simplify the determinant expression After calculating and simplifying the determinant expression, we will express it in terms of \( d \) and \( \sin \theta \). ### Step 4: Find the minimum value of \( \det(A) \) To find the minimum value of \( \det(A) \), we will analyze the expression obtained in the previous step. We will find the critical points by taking the derivative with respect to \( \sin \theta \) and setting it to zero. ### Step 5: Set the minimum value equal to 8 Once we have the expression for the minimum value of \( \det(A) \), we will set it equal to 8: \[ \text{Minimum value of } \det(A) = 8 \] ### Step 6: Solve for \( d \) From the equation obtained in the previous step, we will solve for \( d \). ### Step 7: Conclusion After solving the equation, we will find the possible values of \( d \). ### Final Result The values of \( d \) that satisfy the condition are: \[ d = -5 \quad \text{or} \quad d = 1 \] Thus, the minimum value of \( d \) is \( -5 \). ---
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