  The aim of the thesis is the study of properties of solar flares via
reconstruction of energy distributions of accelerated/heated electrons,
diagnostics of flare plasma based on EUV and X-ray observations, as well as the
estimation of the thermal balance within the "standard" flare model. The X-ray
data were obtained from the Ramaty High Energy Solar Spectroscopic Imager
(RHESSI) and the Russian solar observatory KORONAS-F (IRIS experiment). The EUV
data were obtained from the Solar Dynamics Observatory / Atmospheric Imaging
Assembly (SDO/AIA). In the first chapter a new technique is presented, which
allowed to determine at first the photon spectra based on the KORONAS-F/IRIS
observations and then to reconstruct the energy spectra of the emitting
electrons using the random search method and the Tikhonov regularization
method. In the second chapter the developed technique of simultaneously fitting
the model differential emission measure functions (DEM) to RHESSI and SDO/AIA
data is introduced, which allowed to infer the electron distribution from X-ray
and EUV observations. The proposed method allows to reconstruct of both the
spectra of accelerated/heated electrons and the basic parameters of the flare
plasma, such as temperature, emission measure, total electron number density,
and flare energy. In addition, the analytical function suitable for both DEM
analysis and mean electron flux spectra in flares has been developed and
applied, as well as kappa-distribution in the form of differential emission
measure. The thermal balance and hard X-ray emission of coronal loops from
different flare regions within the "standard" flare model is considered in the
third chapter. This thesis is based on the next papers: Motorina et al., TePh,
2012, Motorina & Kontar, Ge&Ae, 2015, Battaglia et al., ApJ, 2015, Motorina et
al., TePh, 2016, Tsap et al., Ge&Ae, 2016.
