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If A,B,C,P,Q,R in R and Delta=|(cos(A...

If `A,B,C,P,Q,R in R` and
`Delta=|(cos(A+P),cos(A+Q),cos(A+R)),(cos(B+P),cos(B+Q),cos(B+R)),(cos(C+P),cos(C+Q),cos(C+R))|`

A

`Delta` depends on P,Q,R

B

`Delta ` depends on A,B,C

C

`Delta` depends on A,B,C,P,Q,R

D

None of these

Text Solution

AI Generated Solution

The correct Answer is:
To solve the given determinant problem, we need to evaluate the determinant: \[ \Delta = \begin{vmatrix} \cos(A+P) & \cos(A+Q) & \cos(A+R) \\ \cos(B+P) & \cos(B+Q) & \cos(B+R) \\ \cos(C+P) & \cos(C+Q) & \cos(C+R) \end{vmatrix} \] ### Step 1: Apply the Cosine Addition Formula Using the cosine addition formula, we can rewrite each entry of the determinant: \[ \cos(A + P) = \cos A \cos P - \sin A \sin P \] \[ \cos(A + Q) = \cos A \cos Q - \sin A \sin Q \] \[ \cos(A + R) = \cos A \cos R - \sin A \sin R \] Similarly, we can expand the other rows: \[ \cos(B + P) = \cos B \cos P - \sin B \sin P \] \[ \cos(B + Q) = \cos B \cos Q - \sin B \sin Q \] \[ \cos(B + R) = \cos B \cos R - \sin B \sin R \] \[ \cos(C + P) = \cos C \cos P - \sin C \sin P \] \[ \cos(C + Q) = \cos C \cos Q - \sin C \sin Q \] \[ \cos(C + R) = \cos C \cos R - \sin C \sin R \] ### Step 2: Substitute into the Determinant Now, substituting these expressions back into the determinant, we have: \[ \Delta = \begin{vmatrix} \cos A \cos P - \sin A \sin P & \cos A \cos Q - \sin A \sin Q & \cos A \cos R - \sin A \sin R \\ \cos B \cos P - \sin B \sin P & \cos B \cos Q - \sin B \sin Q & \cos B \cos R - \sin B \sin R \\ \cos C \cos P - \sin C \sin P & \cos C \cos Q - \sin C \sin Q & \cos C \cos R - \sin C \sin R \end{vmatrix} \] ### Step 3: Factor Out Common Terms Notice that the first column can be factored out: \[ \Delta = \begin{vmatrix} \cos P & \cos Q & \cos R \\ \cos P & \cos Q & \cos R \\ \cos P & \cos Q & \cos R \end{vmatrix} - \begin{vmatrix} \sin A \sin P & \sin A \sin Q & \sin A \sin R \\ \sin B \sin P & \sin B \sin Q & \sin B \sin R \\ \sin C \sin P & \sin C \sin Q & \sin C \sin R \end{vmatrix} \] ### Step 4: Evaluate the Determinant Now, we can see that the determinant has two rows that are identical in the first matrix, which means: \[ \begin{vmatrix} \cos P & \cos Q & \cos R \\ \cos P & \cos Q & \cos R \\ \cos P & \cos Q & \cos R \end{vmatrix} = 0 \] And similarly, the second determinant will also evaluate to zero due to the same reasoning (the rows are linearly dependent). ### Conclusion Thus, we find that: \[ \Delta = 0 \] ### Final Answer The determinant does not depend on \( A, B, C, P, Q, R \) since it evaluates to zero regardless of their values. Therefore, the correct option is: **None of these.**
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