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What is the value of the determinant ? ...

What is the value of the determinant ?
`|(x+1,x+2,x+4),(x+3,x+5,x+8),(x+7,x+10,x+14)|` ?

A

x + 2

B

`x^(2) + 2`

C

2

D

-2

Text Solution

AI Generated Solution

The correct Answer is:
To find the value of the determinant \[ D = \begin{vmatrix} x+1 & x+2 & x+4 \\ x+3 & x+5 & x+8 \\ x+7 & x+10 & x+14 \end{vmatrix} \] we will perform column operations to simplify the determinant. ### Step 1: Perform Column Operations We will perform the following operations: - \( C_2 \rightarrow C_2 - C_1 \) - \( C_3 \rightarrow C_3 - C_1 \) After applying these operations, the determinant becomes: \[ D = \begin{vmatrix} x+1 & (x+2)-(x+1) & (x+4)-(x+1) \\ x+3 & (x+5)-(x+3) & (x+8)-(x+3) \\ x+7 & (x+10)-(x+7) & (x+14)-(x+7) \end{vmatrix} \] Calculating the new values in the second and third columns: - For \( C_2 \): - \( x+2 - (x+1) = 1 \) - \( x+5 - (x+3) = 2 \) - \( x+10 - (x+7) = 3 \) - For \( C_3 \): - \( x+4 - (x+1) = 3 \) - \( x+8 - (x+3) = 5 \) - \( x+14 - (x+7) = 7 \) Thus, the determinant simplifies to: \[ D = \begin{vmatrix} x+1 & 1 & 3 \\ x+3 & 2 & 5 \\ x+7 & 3 & 7 \end{vmatrix} \] ### Step 2: Expand the Determinant Now we will expand the determinant along the first row: \[ D = (x+1) \begin{vmatrix} 2 & 5 \\ 3 & 7 \end{vmatrix} - 1 \begin{vmatrix} x+3 & 5 \\ x+7 & 7 \end{vmatrix} + 3 \begin{vmatrix} x+3 & 2 \\ x+7 & 3 \end{vmatrix} \] Calculating the 2x2 determinants: 1. \( \begin{vmatrix} 2 & 5 \\ 3 & 7 \end{vmatrix} = (2)(7) - (5)(3) = 14 - 15 = -1 \) 2. \( \begin{vmatrix} x+3 & 5 \\ x+7 & 7 \end{vmatrix} = (x+3)(7) - (5)(x+7) = 7x + 21 - 5x - 35 = 2x - 14 \) 3. \( \begin{vmatrix} x+3 & 2 \\ x+7 & 3 \end{vmatrix} = (x+3)(3) - (2)(x+7) = 3x + 9 - 2x - 14 = x - 5 \) Now substituting these back into the determinant expansion: \[ D = (x+1)(-1) - 1(2x - 14) + 3(x - 5) \] ### Step 3: Simplify the Expression Now we simplify: \[ D = -(x + 1) - (2x - 14) + 3(x - 5) \] \[ = -x - 1 - 2x + 14 + 3x - 15 \] \[ = (-x - 2x + 3x) + (-1 + 14 - 15) \] \[ = 0 + (-2) = -2 \] ### Final Result Thus, the value of the determinant is: \[ \boxed{-2} \]
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