In this poster, we present two contrasting studies: First, we want to investigate the hypothesis that non-linear interactions in the power spectra of δ Scuti stars are related to their evolutionary state. For this purpose, we examine a set of light curves belonging to a sample of young δ Scuti stars observed by the TESS satellite. We expect an absence of sum combinations in them, and the results agree with such an assumption. The second study outlines the procedure of numerically solving the non-linear differential equations of oscillations for High Amplitude Delta Scuti (HADS) stars. The equations are described in terms of the so-called Volterra expansion, and these coefficients can be estimated observationally through amplitude and phase relations between parents and children frequencies (see Lares-Martiz et al. 2020). After obtaining these coefficients, the equations can be numerically solved.