An equation of electric potential of a particle P separated from a uniformly charged flat plate was theoretically derived. An equation of electric field was also introduced from this equation. The electric potential is expressed by equation comprised of the logarithmic function and tangential inverse trigonometric function, which include elements (i.e. oblique line and sides of a base) of the quadrangular pyramid PABCO created by connecting the point P with respective vertexes of a rectangle and irrational function. The equation of the electric potential produced when the point P is just above the center of the flat plate is expressed as equation four times the equation symmetric with respect to a and b which are lengths of the sides in the base of the pyramid
Keywords: electric field by flat plate, electric potential by flat plate, theoretical analysis of complex double integration
