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If x=4x = -4 is a root of x231x132x=0\begin{vmatrix}x & 2 & 3 \\ 1 & x & 1 \\ 3 & 2 & x\end{vmatrix} = 0, then the sum of the other 2 roots is

Solution

Correct Option: 1

Given that x=4x = -4 is a root of x231x132x=0\begin{vmatrix}x & 2 & 3 \\ 1 & x & 1 \\ 3 & 2 & x\end{vmatrix} = 0

Expanding the determinant using the first row:

xx12x2113x+31x32=0x \begin{vmatrix}x & 1 \\ 2 & x\end{vmatrix} - 2 \begin{vmatrix}1 & 1 \\ 3 & x\end{vmatrix} + 3 \begin{vmatrix}1 & x \\ 3 & 2\end{vmatrix} = 0


Computing each 2×2 determinant:

x12x=x22\begin{vmatrix}x & 1 \\ 2 & x\end{vmatrix} = x^2 - 2

113x=x3\begin{vmatrix}1 & 1 \\ 3 & x\end{vmatrix} = x - 3

1x32=23x\begin{vmatrix}1 & x \\ 3 & 2\end{vmatrix} = 2 - 3x


Substituting back:

x(x22)2(x3)+3(23x)=0x(x^2 - 2) - 2(x - 3) + 3(2 - 3x) = 0

x32x2x+6+69x=0x^3 - 2x - 2x + 6 + 6 - 9x = 0

x313x+12=0x^3 - 13x + 12 = 0


For a cubic equation x3+bx2+cx+d=0x^3 + bx^2 + cx + d = 0, the sum of all roots equals b-b.

The equation is: x3+0x213x+12=0x^3 + 0x^2 - 13x + 12 = 0

Sum of all three roots =0=0= -0 = 0


Given one root is x=4x = -4:

(4)+(sum of other two roots)=0(-4) + \text{(sum of other two roots)} = 0

Sum of other two roots =4= 4

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