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If A=[123x2y41610]A = \begin{bmatrix} -1 & 2 & 3x \\ 2y & 4 & -1 \\ 6 & -1 & 0 \end{bmatrix} is a symmetric matrix, then the value of 2xy2x - y is:

Solution

Correct Option: 3

For a symmetric matrix, the element at position (row i, column j) equals the element at position (row j, column i).

Given matrix:

A=[123x2y41610]A = \begin{bmatrix} -1 & 2 & 3x \\ 2y & 4 & -1 \\ 6 & -1 & 0 \end{bmatrix}

Position (1,2) = 2

Position (2,1) = 2y

Position (1,3) = 3x

Position (3,1) = 6


Since the matrix is symmetric, the mirror positions must be equal.

Comparing position (1,2) with position (2,1):

2=2y2 = 2y

y=1y = 1


Comparing position (1,3) with position (3,1):

3x=63x = 6

x=2x = 2


The value of 2xy2x - y:

2xy=2(2)12x - y = 2(2) - 1

2xy=412x - y = 4 - 1

2xy=32x - y = 3

Therefore, the value of 2xy2x - y is 33.

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