If ∣110x2+2x+210211∣=0\left|\begin{array}{ccc}1 & 1 & 0 \\x^2+2 x+2 & 1 & 0 \\2 & 1 & 1\end{array}\right|=01x2+2x+22111001
Question
If 1x2+2x+22111001=0, then the value of x is
A.
2
B.
-2
C.
1
D.
-1
Correct option is D
Let the matrix be:Δ=1x2+2x+22111011We can expand along the third column since it has two zeros, making the calculation easier.Δ=0⋅M13−1⋅M23+1⋅M33Where Mij is the minor of element (i,j), i.e., determinant of the 2×2 matrix formed by deleting the ith rowand jth column:M33=1x2+2x+211=(1)(1)−(1)(x2+2x+2)=1−(x2+2x+2)=1−x2−2x−2=−x2−2x−1Thus:Δ=−(1⋅1211)+1⋅1x2+2x+211)Δ=−(1⋅1−1⋅2)+(1⋅1−1⋅(x2+2x+2))Δ=−(1−2)+(1−x2−2x−2)Δ=−(−1)+(−x2−2x−1)Δ=1−x2−2x−1Δ=−x2−2xSet determinant to zero:−x2−2x=0⟹x2+2x=0⟹x(x+2)=0⟹x=0 or x=−2