\documentclass[a4j]{jarticle} \begin{document} $e^{i \theta}=\cos \theta+i \sin \theta$ \end{document}

\documentclass[a4j]{jarticle} \begin{document} $p=\hbar k=\frac{h}{\lambda}$ \end{document}

\documentclass[a4j]{jarticle} \begin{document} $-\frac{\hbar^{2}}{2 m} \Delta \psi(\vec{r}, t)=i \hbar \frac{\partial \psi(\vec{r}, t)}{\partial t}$ \end{document}