Answer:
The value of a=4
Step-by-step explanation:
Given the matrix
[tex]B=\begin{pmatrix}1\:&\:2\:\\ \:\:\:2\:&\:a\end{pmatrix}[/tex]
so solving the matrix B by taking its determinant to get the value a
[tex]\det \begin{pmatrix}1&2\\ 2&a\end{pmatrix}=0[/tex]
as according to determinant formula
[tex]\det \begin{pmatrix}a\:&\:b\:\\ c\:&\:d\:\end{pmatrix}\:=\:ad-bc[/tex]
[tex]1\cdot \:a-2\cdot \:2=0[/tex]
[tex]a-4=0[/tex]
[tex]a=4[/tex]
Therefore, the value of a=4
