Question

linear algebra question?
This is a sample question, but I couldn't simplify it，Please give a hand，thx！

Answer 1

First multiply them together 
$\left[\begin{array}{ccc}a-6&2&ab\\2&1&5b\\-3&1+3b&2\end{array}\right]$

A symmetric matrix is where the transpose is equal to original matrix.

This means row n = column n
Looking at row1 = column1 ----> ab = -3
Looking at row2 =column2 ----> 5b = 1+3b

Solve those 2 equations for a,b

b = 1/2
a = -6