  The family of functions, we investigate in this article, was originally
introduced by A.Denjoy and later rediscovered by R Tichy and J. Uitz. We denote
the functions of the family by $g_{\lambda}(x),$ where $\lambda\in(0,1)$. The
definition will be given in the following section. The most famous function of
the family is the Minkiowski question-mark function. As we would see, it
corresponds to $\lambda=\frac12$. All functions of the family are continuous,
strictly increasing and map the segment $[0,1]$ onto itself. Moreover, they are
singular i.e. $\forall \lambda$ the derivative $g'_{\lambda}(x),$ if exists,
can take only two values: 0 and $+\infty.$ In this paper we consider two
functions of the class which correspond to $\lambda$ equals $\frac{\sqrt5-1}2$
or $1-\frac{\sqrt5-1}2.$ The aim of this paper is to prove some theorems about
essential conditions on x such that if the condition holds then the derivative
$g'_{\lambda}(x)$ exists and has determined value. The constants used in our
theorems are non-improvable.
  Our paper is wirtten in Russian. However Introduction and the formulation of
main results are written in English.
