Welcome to the forum! Please read this topic
to learn how to post code in code or highlight tags and other useful info for new members.
Start by defining what a symmetric matrix is and then think about how you'd look at a matrix and use your brain to determine if it's symmetric. Do that a few times (look and decide) and then write down how your brain made the decision. Once you've written it down and believe it's correct, use what you've written down as comments to guide your code. Then write the code that goes with the comments.