If the matrix $A=\left[\begin{array}{rcr}3 & 2 a & -5 \\ -4 & 0 & b \\ -5 & 3 & 7\end{array}\right]$ is symmetric then the value of (a + b) is
Answer & explanation
Correct answer: option 1
Let $A=\left[\begin{array}{rcr}3 & 2 a & -5 \\ -4 & 0 & b \\ -5 & 3 & 7\end{array}\right]$
⇒ A is symmetric matrix, so, A = A'
$\left[\begin{array}{rcr}3 & 2 a & -5 \\ -4 & 0 & b \\ -5 & 3 & 7\end{array}\right]$=$\left[\begin{array}{rcr}3 & -4 & -5 \\ 2a & 0 & 3 \\ -5 & b & 7\end{array}\right]$
2a = -4, b = 3
$a = \frac{-4}{2}$
a = -2
∴ a + b = -2 + 3 = 1