In our joint papers [FL1-FL2] we revive quaternionic analysis and show deep relations between quaternionic analysis, representation theory and four-dimensional physics. As a guiding principle we use representation theory of various real forms of the conformal group. We demonstrate that the requirement of unitarity of representations naturally leads us to the extensions of the Cauchy-Fueter and Poisson formulas to the Minkowski space, which can be viewed as another real form of quaternions. However, the Minkowski space formulation also brings some technical difficulties related to the fact that the singularities of the kernels in these integral formulas are now concentrated on the light cone instead of just a single point in the initial quaternionic picture. But the same phenomenon occurs when one passes from the complex numbers to the split complex numbers (or hyperbolic algebra). So, as a warm-up example we proved an analogue of the Cauchy integral formula for the split complex numbers. On the other hand, there seems to be sufficient interest in such formula among physicists. For example, see [KS] and the references therein.