TeX source:

\begin{array}{rcl}\mathbb{D} &=& \mathbb{R}\times\mathbb{R}\setminus_{\{0\}} \\\\g(x,y) &=& \dfrac{7\cos(x)}{10y}+19xy-0{,}851 \\&=& \dfrac{7}{10} \cos(x)\cdot y^{-1}+19xy-0{,}851\end{array}