(Concrete cases from 2.) Change to vector-matrix form and discuss the stability of the trivial solution of the following equations.
- \(u''-u=0\)
- \(u''+2ku'+u=0\) with \(k>0\)
- \(u^{(4)}+2u''+u=0\)
- \(y'=\Theta y\) where \(\Theta \) is the matrix of all zeros.