IIRC, your spoilery “so” is the other way round. The right side is the definition, and the left-hand side a layman’s shorthand, as the root operator isn’t defined on negative numbers.
I might very well be wrong. My being a mathematician has been over for a while now, my being a pedantic PITA not though.
Thanks to Tactics I hugely got into XCOM later, and I still hope for some kind of proper remake or sequel.