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If alpha is a non-real cube root of -2, ...

If `alpha` is a non-real cube root of `-2`, then the value of `|(1,2 alpha,1),(alpha^(2),1,3 alpha^(2)),(2,2 alpha,1)|`, is

A

`-11`

B

`-12`

C

`-13`

D

0

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The correct Answer is:
To solve the determinant \( D = \begin{vmatrix} 1 & 2\alpha & 1 \\ \alpha^2 & 1 & 3\alpha^2 \\ 2 & 2\alpha & 1 \end{vmatrix} \), where \( \alpha \) is a non-real cube root of \(-2\), we will follow these steps: ### Step 1: Write down the determinant We start with the determinant: \[ D = \begin{vmatrix} 1 & 2\alpha & 1 \\ \alpha^2 & 1 & 3\alpha^2 \\ 2 & 2\alpha & 1 \end{vmatrix} \] ### Step 2: Expand the determinant using the first row We will expand the determinant using the first row. The formula for the determinant of a 3x3 matrix is: \[ D = a(ei - fh) - b(di - fg) + c(dh - eg) \] For our matrix, we have: - \( a = 1 \), \( b = 2\alpha \), \( c = 1 \) - The remaining elements are: - \( d = \alpha^2 \), \( e = 1 \), \( f = 3\alpha^2 \) - \( g = 2 \), \( h = 2\alpha \), \( i = 1 \) Thus, we calculate: \[ D = 1 \cdot (1 \cdot 1 - 3\alpha^2 \cdot 2\alpha) - 2\alpha \cdot (\alpha^2 \cdot 1 - 3\alpha^2 \cdot 2) + 1 \cdot (\alpha^2 \cdot 2\alpha - 1 \cdot 2) \] ### Step 3: Calculate each part Calculating each term: 1. First term: \[ 1 \cdot (1 - 6\alpha^3) \] 2. Second term: \[ - 2\alpha \cdot (\alpha^2 - 6\alpha^2) = -2\alpha \cdot (-5\alpha^2) = 10\alpha^3 \] 3. Third term: \[ 2\alpha^3 - 2 \] ### Step 4: Combine all terms Now we combine all the terms: \[ D = (1 - 6\alpha^3) + 10\alpha^3 + (2\alpha^3 - 2) \] Combining like terms: \[ D = 1 - 2 - 6\alpha^3 + 10\alpha^3 + 2\alpha^3 \] This simplifies to: \[ D = -1 + 6\alpha^3 \] ### Step 5: Substitute the value of \( \alpha^3 \) Since \( \alpha \) is a cube root of \(-2\), we have: \[ \alpha^3 = -2 \] Substituting this into our expression for \( D \): \[ D = -1 + 6(-2) = -1 - 12 = -13 \] ### Final Answer Thus, the value of the determinant is: \[ \boxed{-13} \]

To solve the determinant \( D = \begin{vmatrix} 1 & 2\alpha & 1 \\ \alpha^2 & 1 & 3\alpha^2 \\ 2 & 2\alpha & 1 \end{vmatrix} \), where \( \alpha \) is a non-real cube root of \(-2\), we will follow these steps: ### Step 1: Write down the determinant We start with the determinant: \[ D = \begin{vmatrix} 1 & 2\alpha & 1 \\ \alpha^2 & 1 & 3\alpha^2 \\ 2 & 2\alpha & 1 \end{vmatrix} \] ...
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OBJECTIVE RD SHARMA ENGLISH-DETERMINANTS-Section I - Solved Mcqs
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