Solve a math problem?

[emt1]

I was wondering if someone who's good at math good solve the following math problem for me. I'd really appreciate it! Thanks!

Obviously, I'm solving for σ

 

[sammich]

I'm not going to solve it for you but have you tried taking a +/- of the RHS to get around the abs brackets? The problem then becomes trivial.

You could square both sides, but it's just extra work.