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If D=|{:(2,1,[sin^2theta]),([sin^2theta]...

If `D=|{:(2,1,[sin^2theta]),([sin^2theta],costheta,i),(i,1,sintheta):}|`
(here[.] is greatest function and `i=sqrt(-1)` , then arg (D) `in`

A

`{-tan^(-1)2,-pi+tan^(-1)2}`

B

`((-3pi)/4,(-pi)/2)cup{tan^(-1)2,-pi+tan^(-1)2}`

C

`[(-3pi)/4,(-pi)/2]`

D

none of these

Text Solution

AI Generated Solution

The correct Answer is:
To solve the problem, we need to evaluate the determinant \( D \) and find its argument \( \arg(D) \). Given: \[ D = \begin{vmatrix} 2 & 1 & \lfloor \sin^2 \theta \rfloor \\ \lfloor \sin^2 \theta \rfloor & \cos \theta & i \\ i & 1 & \sin \theta \end{vmatrix} \] ### Step 1: Determine the value of \( \lfloor \sin^2 \theta \rfloor \) The value of \( \sin^2 \theta \) ranges from 0 to 1. Therefore, the greatest integer function \( \lfloor \sin^2 \theta \rfloor \) can take the following values: - If \( 0 \leq \sin^2 \theta < 1 \), then \( \lfloor \sin^2 \theta \rfloor = 0 \). - If \( \sin^2 \theta = 1 \) (which occurs when \( \theta = \frac{\pi}{2} + 2n\pi \)), then \( \lfloor \sin^2 \theta \rfloor = 1 \). ### Step 2: Case Analysis #### Case 1: \( \theta \neq \frac{\pi}{2} + 2n\pi \) In this case, \( \lfloor \sin^2 \theta \rfloor = 0 \). The determinant simplifies to: \[ D = \begin{vmatrix} 2 & 1 & 0 \\ 0 & \cos \theta & i \\ i & 1 & \sin \theta \end{vmatrix} \] #### Step 3: Calculate the determinant Using the determinant formula: \[ D = 2 \begin{vmatrix} \cos \theta & i \\ 1 & \sin \theta \end{vmatrix} - 1 \begin{vmatrix} 0 & i \\ i & \sin \theta \end{vmatrix} \] Calculating the first determinant: \[ \begin{vmatrix} \cos \theta & i \\ 1 & \sin \theta \end{vmatrix} = \cos \theta \sin \theta - i \] Calculating the second determinant: \[ \begin{vmatrix} 0 & i \\ i & \sin \theta \end{vmatrix} = 0 - i^2 = 1 \] Thus, we have: \[ D = 2(\cos \theta \sin \theta - i) - 1 = 2\cos \theta \sin \theta - 2i - 1 \] \[ D = 2\cos \theta \sin \theta - 1 - 2i \] ### Step 4: Find the argument of \( D \) Let \( z = 2\cos \theta \sin \theta - 1 - 2i \). The argument \( \arg(z) \) can be computed as: \[ \arg(z) = \tan^{-1}\left(\frac{\text{Im}(z)}{\text{Re}(z)}\right) = \tan^{-1}\left(\frac{-2}{2\cos \theta \sin \theta - 1}\right) \] ### Step 5: Case 2: \( \theta = \frac{\pi}{2} + 2n\pi \) In this case, \( \lfloor \sin^2 \theta \rfloor = 1 \). The determinant simplifies to: \[ D = \begin{vmatrix} 2 & 1 & 1 \\ 1 & \cos \theta & i \\ i & 1 & \sin \theta \end{vmatrix} \] Calculating this determinant similarly will yield a different expression for \( D \). ### Conclusion The argument of \( D \) will depend on the value of \( \theta \). For \( \theta \neq \frac{\pi}{2} + 2n\pi \), we have: \[ \arg(D) = \tan^{-1}\left(\frac{-2}{2\cos \theta \sin \theta - 1}\right) \] For \( \theta = \frac{\pi}{2} + 2n\pi \), the determinant simplifies to a different form, and we need to evaluate that separately.
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