Hence, there are three possible cases of roots, namely 1. Distinct real roots ( ): Characteristic equation can be represented in the form , the general solution of Eq. (11.7) can be represented in the form . 2. Real and repeated roots ( ): Characteristic equation can be represented in the form , the general solution of Eq. (11.7) can be represented in the form where and . 3. Complex conjugate roots ( ): Recall Euler relation of complex exponential, namely where symbol √ represent unit imaginary number. General solution of Eq. (11.7) can be represented in the form [ ].