Incorrect or non-functional Latex display

[Defennder]

I don't know if it's just me, but the latex code I've entered in https://www.physicsforums.com/showthread.php?t=242141" doesn't display at all, instead it's replaced by the invalid latex code red message. I checked the syntax and it seems to be all right. When I copied the Latex code and previewed in a post reply, the latex image that shows up appeared to be an earlier latex image which I posted elsewhere. What's causing this problem?

 

[Defennder]

Okay nevermind I just tried out the latex code elsewhere and found that I neglected to close some braces. It looks okay now.