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The value/s of 'λ\lambda' for which the system of equations

λx+3y−z=1\lambda x + 3y - z = 1

x+2y+z=2x + 2y + z = 2

−λx+y+2z=−1-\lambda x + y + 2z = -1

has unique solution is/are:

(where RR is set of real numbers)

Solution

✅ Correct Option: 4

A unique solution exists when the coefficient determinant is non-zero.

Expanding, Δ=λ(4−1)−3(2+λ)−(1+2λ)=3λ−6−3λ−1−2λ=−2λ−7\Delta = \lambda(4-1)-3(2+\lambda)-(1+2\lambda) = 3\lambda-6-3\lambda-1-2\lambda = -2\lambda-7.

Setting Δ=0\Delta = 0 gives λ=−72\lambda = -\dfrac{7}{2}, so the system has a unique solution for all λ∈R−{−72}\lambda \in R-\left\{-\dfrac{7}{2}\right\}.

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