If A = ((1,λ,2),(1,2,5),(2,1,1)) is not invertible then λ = ? ​

Question

If A = \(\begin{pmatrix} 3&λ&2 \\ 1 &2&5\\2&1&1 \end{pmatrix}\) is not invertible then λ = ?

A. 2 

B. 1 

C. -1 

D. 0

Answer 1

= \(\begin{pmatrix} 3&λ&2 \\ 1 &2&5\\2&1&1 \end{pmatrix}\)

│A│= 0 

1(2 x 1 – 5 x 1) - (1 x 1 – 5 x 2) + 2 ( 1 x 1 – 2 x 2) = 0 

-3 + 9 λ - 6 = 0 

9 λ = 9 

λ = 1