Compared to contemporary texts like Zill or Boyce & DiPrima, Kells is more concise.
Kells provides a robust treatment of linear equations of higher order. The methodology is traditional: reduction of order, undetermined coefficients, and variation of parameters. The strength here is the clarity in handling the "Operator Methods" (Métodos de operadores), which simplifies the algebraic manipulation of differential operators for engineering students. Ecuaciones-diferenciales-elementales-kells-pdf