Interpret the determinant equation
We have
∣ x + 1 x x x x + λ x x x x + λ 2 ∣ = 9 8 ( 103 x + 81 ) . \begin{vmatrix}
x+1 & x & x\\
x & x+\lambda & x\\
x & x & x+\lambda^2
\end{vmatrix}
= \frac{9}{8}(103x+81). x + 1 x x x x + λ x x x x + λ 2 = 8 9 ( 103 x + 81 ) .
We first simplify the determinant.
Write the matrix in a convenient form
Observe that the matrix is
( x + 1 x x x x + λ x x x x + λ 2 ) = ( 1 0 0 0 λ 0 0 0 λ 2 ) + ( x x x x x x x x x ) . \begin{pmatrix}
x+1 & x & x\\
x & x+\lambda & x\\
x & x & x+\lambda^2
\end{pmatrix}
=
\begin{pmatrix}
1 & 0 & 0\\
0 & \lambda & 0\\
0 & 0 & \lambda^2
\end{pmatrix}
+
\begin{pmatrix}
x & x & x\\
x & x & x\\
x & x & x
\end{pmatrix}. x + 1 x x x x + λ x x x x + λ 2 = 1 0 0 0 λ 0 0 0 λ 2 + x x x x x x x x x .
So this is of the form
D + x J , D + xJ, D + x J ,
where
D = diag ( 1 , λ , λ 2 ) , J = ( 1 1 1 1 1 1 1 1 1 ) . D=\operatorname{diag}(1,\lambda,\lambda^2), \qquad J=\begin{pmatrix}1&1&1\\1&1&1\\1&1&1\end{pmatrix}. D = diag ( 1 , λ , λ 2 ) , J = 1 1 1 1 1 1 1 1 1 .
But it is easier here to expand directly.
Compute the determinant
Let
Δ = ∣ x + 1 x x x x + λ x x x x + λ 2 ∣ . \Delta=
\begin{vmatrix}
x+1 & x & x\\
x & x+\lambda & x\\
x & x & x+\lambda^2
\end{vmatrix}. Δ = x + 1 x x x x + λ x x x x + λ 2 .
Apply row operations:
R 2 → R 2 − R 1 , R 3 → R 3 − R 1 . R_2 \to R_2-R_1, \qquad R_3 \to R_3-R_1. R 2 → R 2 − R 1 , R 3 → R 3 − R 1 .
Then
Δ = ∣ x + 1 x x − 1 λ 0 − 1 0 λ 2 ∣ . \Delta=
\begin{vmatrix}
x+1 & x & x\\
-1 & \lambda & 0\\
-1 & 0 & \lambda^2
\end{vmatrix}. Δ = x + 1 − 1 − 1 x λ 0 x 0 λ 2 .
Now expand along the first row:
Δ = ( x + 1 ) ∣ λ 0 0 λ 2 ∣ − x ∣ − 1 0 − 1 λ 2 ∣ + x ∣ − 1 λ − 1 0 ∣ . \Delta=(x+1)
\begin{vmatrix}
\lambda & 0\\
0 & \lambda^2
\end{vmatrix}
-x
\begin{vmatrix}
-1 & 0\\
-1 & \lambda^2
\end{vmatrix}
+x
\begin{vmatrix}
-1 & \lambda\\
-1 & 0
\end{vmatrix}. Δ = ( x + 1 ) λ 0 0 λ 2 − x − 1 − 1 0 λ 2 + x − 1 − 1 λ 0 .
Compute each minor:
∣ λ 0 0 λ 2 ∣ = λ 3 , \begin{vmatrix}
\lambda & 0\\
0 & \lambda^2
\end{vmatrix}=\lambda^3, λ 0 0 λ 2 = λ 3 ,
∣ − 1 0 − 1 λ 2 ∣ = − λ 2 , \begin{vmatrix}
-1 & 0\\
-1 & \lambda^2
\end{vmatrix}=-\lambda^2, − 1 − 1 0 λ 2 = − λ 2 ,
∣ − 1 λ − 1 0 ∣ = λ . \begin{vmatrix}
-1 & \lambda\\
-1 & 0
\end{vmatrix}=\lambda. − 1 − 1 λ 0 = λ .
Hence
Δ = ( x + 1 ) λ 3 − x ( − λ 2 ) + x λ = λ 3 x + λ 3 + x λ 2 + x λ . \Delta=(x+1)\lambda^3-x(-\lambda^2)+x\lambda
=\lambda^3 x+\lambda^3+x\lambda^2+x\lambda. Δ = ( x + 1 ) λ 3 − x ( − λ 2 ) + x λ = λ 3 x + λ 3 + x λ 2 + x λ .
So
Δ = x ( λ 3 + λ 2 + λ ) + λ 3 . \Delta=x(\lambda^3+\lambda^2+\lambda)+\lambda^3. Δ = x ( λ 3 + λ 2 + λ ) + λ 3 .
Compare coefficients with the given RHS
Given
Δ = 9 8 ( 103 x + 81 ) = 927 8 x + 729 8 . \Delta=\frac{9}{8}(103x+81)=\frac{927}{8}x+\frac{729}{8}. Δ = 8 9 ( 103 x + 81 ) = 8 927 x + 8 729 .
Therefore,
λ 3 = 729 8 . \lambda^3=\frac{729}{8}. λ 3 = 8 729 .
So
λ = 9 2 . \lambda=\frac{9}{2}. λ = 2 9 .
Also,
λ 3 + λ 2 + λ = 927 8 . \lambda^3+\lambda^2+\lambda=\frac{927}{8}. λ 3 + λ 2 + λ = 8 927 .
Check with λ = 9 2 \lambda=\frac92 λ = 2 9 :
λ 3 + λ 2 + λ = 729 8 + 81 4 + 9 2 = 729 + 162 + 36 8 = 927 8 , \lambda^3+\lambda^2+\lambda
=\frac{729}{8}+\frac{81}{4}+\frac92
=\frac{729+162+36}{8}
=\frac{927}{8}, λ 3 + λ 2 + λ = 8 729 + 4 81 + 2 9 = 8 729 + 162 + 36 = 8 927 ,
which matches.
So the two numbers are
λ = 9 2 , λ 3 = 3 2 . \lambda=\frac92, \qquad \frac{\lambda}{3}=\frac32. λ = 2 9 , 3 λ = 2 3 .
Form the quadratic whose roots are λ \lambda λ and λ / 3 \lambda/3 λ /3
Roots are
9 2 , 3 2 . \frac92, \frac32. 2 9 , 2 3 .
Their sum is
9 2 + 3 2 = 6 , \frac92+\frac32=6, 2 9 + 2 3 = 6 ,
and product is
9 2 ⋅ 3 2 = 27 4 . \frac92\cdot\frac32=\frac{27}{4}. 2 9 ⋅ 2 3 = 4 27 .
Hence the quadratic is
x 2 − 6 x + 27 4 = 0. x^2-6x+\frac{27}{4}=0. x 2 − 6 x + 4 27 = 0.
Multiplying by 4,
4 x 2 − 24 x + 27 = 0. 4x^2-24x+27=0. 4 x 2 − 24 x + 27 = 0.
Match with the options
This corresponds to:
Option B:
4 x 2 − 24 x + 27 = 0. 4x^2-24x+27=0. 4 x 2 − 24 x + 27 = 0.
Compare with stored correct answer
Stored correct answer is B , which matches our derived answer.