Given that \(s\) and \(t\) equals
and \(p\) and \(q\) such that
Manipulating a little bit, \(T\) should become
See how \(T\) and \(S\) have a \(\pm\) in them? When you subtract \(s\) from \(t\), why does that \(\pm\) disappear, and does it equal to the same value as when they have the \(\pm\) sign in them?
If you want to see this website, it is: Deriving the Cubic Formula