Often, for the construction of approximate analytical solutions for the components of the stress-strain state (SSS) of an elastic body, series on various systems of functions including trigonometric ones are used. They converge rapidly at the interior points of the elastic body while in the neighborhood of the boundary the rate of their convergence may decrease, and especially at singular points of the boundary, for example, at the corner points. In the paper the rate of convergence of the series in two general solutions for an elastic isotropic rectangle at the corner point is considered. Two solutions are built on the basis of two different continuations of the solution beyond the boundaries of the body: an even and an odd one.