1.

If \(\begin{bmatrix} 1 & -4 & 3 \\\ 0 & 6 & -7 \\\ 2 & 4 & λ \end{bmatrix}\) is not an invertible matrix, then what is the value of λ ?

Answer» Correct Answer - Option 3 : -8

Concept:

If A is not an invertible matrix then |A| = 0

If A is a singular matrix then |A| = 0

Calculation:

Given A =  \(\begin{bmatrix} 1 & -4 & 3 \\\ 0 & 6 & -7 \\\ 2 & 4 & λ \end{bmatrix}\) is not an invertible matrix.

⇒ A is a singular matrix.

⇒ |A| = 0

⇒ \(\begin{vmatrix} 1 & -4 & 3 \\\ 0 & 6 & -7 \\\ 2 & 4 & λ \end{vmatrix}\) = 0

⇒ 1(\(\rm 6\lambda + 28 \)) + 4 (0 + 14) + 3 (0 - 12) = 0

⇒  \(\rm 6\lambda + 28 + 56 - 36 = 0\)

⇒ \(\rm 6\lambda + 48 = 0\)

⇒ \(\rm \lambda = - 8\)

Hence, if \(\begin{bmatrix} 1 & -4 & 3 \\\ 0 & 6 & -7 \\\ 2 & 4 & λ \end{bmatrix}\) is not an invertible matrix, then the value of λ = - 8



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