Which of the following is the differential equation whose solution is \[y = a { e }^{ x } + b { e }^{ -x } \]

y'+y= 0 y'-y = 0 y'' +y = 0 y'' - y = 0

y'' - y = 0

y' = \(a { e }^{ x } - b { e }^{- x } \) \(Rightarrow y'' = a { e }^{ x } + b { e }^{- x } \) $\Rightarrow y'' = y$ $\Rightarrow y'' - y = 0$