Sami H i gazi Mustafa2018-09-202018-09-202004http://hdl.handle.net/123456789/12781In this research we utilize the symmetry condition of differential equations to solve some of these equations . Also we show how Lie algebra methods are much advanced for understanding and unifying all classical methods of solving differential equations . At the end of our research we discuss the variational methods and Euler — Lagrange equations on the light of symmetryenDifference equationsMATHEMATICS -- Differential EquationsMATHEMATICS -- AppliedDifferential equationThesis