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If y=−4y = -4 is a root of ∣y231y132y∣=0\begin{vmatrix} y & 2 & 3 \\ 1 & y & 1 \\ 3 & 2 & y \end{vmatrix} = 0, then the product of the other two roots is

Solution

✅ Correct Option: 4

The determinant equation is:

∣y231y132y∣=0\begin{vmatrix} y & 2 & 3 \\ 1 & y & 1 \\ 3 & 2 & y \end{vmatrix} = 0

Expanding along the first row:

=y∣y12y∣−2∣113y∣+3∣1y32∣= y \begin{vmatrix} y & 1 \\ 2 & y \end{vmatrix} - 2 \begin{vmatrix} 1 & 1 \\ 3 & y \end{vmatrix} + 3 \begin{vmatrix} 1 & y \\ 3 & 2 \end{vmatrix}

=y(y2−2)−2(y−3)+3(2−3y)= y(y^2 - 2) - 2(y - 3) + 3(2 - 3y)

=y3−2y−2y+6+6−9y= y^3 - 2y - 2y + 6 + 6 - 9y

=y3−13y+12= y^3 - 13y + 12

=0= 0


For a cubic equation y3+ay2+by+c=0y^3 + ay^2 + by + c = 0 with roots α,β,γ\alpha, \beta, \gamma, Vieta's formula states:

α×β×γ=−c\alpha \times \beta \times \gamma = -c

The equation is y3+0y2−13y+12=0y^3 + 0y^2 - 13y + 12 = 0, so c=12c = 12.

Product of all three roots =−12= -12


If the three roots are −4,α,β-4, \alpha, \beta, then:

(−4)×α×β=−12(-4) \times \alpha \times \beta = -12

α×β=−12−4\alpha \times \beta = \dfrac{-12}{-4}

α×β=3\alpha \times \beta = 3

Therefore, the product of the other two roots is 33.

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