If the matrix $\begin{bmatrix}3 & 2a& -5\\-4 & 0 & b\\-5 & 3 & 7\end{bmatrix}$ is symmetric, then the value of (a + b) is :

1

The correct answer is Option (2) → 1

$A=\begin{bmatrix}3 & 2a& -5\\-4 & 0 & b\\-5 & 3 & 7\end{bmatrix}$

$A=A^T⇒\begin{bmatrix}3 & -4& -5\\2a & 0 & 3\\-6 & b & 7\end{bmatrix}=\begin{bmatrix}3 & 2a& -5\\-4 & 0 & b\\-5 & 3 & 7\end{bmatrix}$

So on comparison $a=-2,b=3$

$a+b=1$