Here is my latex code:
\begin{document}
\begin{align*}
f_{Y_2}(y_2) &= \int_{\frac{1-\sqrt{2(-1+3y_2)}}{3}}^{1}\frac{1}{4\sqrt{R}} \mathrm{d}y_1 + \int_{0}^{1-\sqrt{-1+2y_2}}\frac{1}{4\sqrt{R}} \mathrm{d}y_1 \\
f_{Y_2}(y_2) &= \frac{1}{2\sqrt{3}} \left[\arcsin \left(\frac{1}{\sqrt{\frac{1}{4} + \frac{3}{2}(y_2-\frac{1}{2})}} \right) - \arcsin \left( \frac{-\sqrt{2(-1+3y_2)}}{2\sqrt{\frac{1}{4} + \frac{3}{2}(y_2-\frac{1}{2})}} \right) + \arcsin \left(\frac{1-\frac{3}{2}\sqrt{-1+2y_2}}{\sqrt{\frac{1}{4} + \frac{3}{2}(y_2-\frac{1}{2})}} - \arcsin \left(\frac{-1}{2\sqrt{\frac{1}{4} + \frac{3}{2}(y_2-\frac{1}{2})}} \right) \right]
\end{align*}

\left. – Apr 24 '19 at 15:21\right)seems to be missing before the last\arcsin.... – Apr 24 '19 at 15:23\intalso\limitsyou certainly will have more space when you write the integranda function. See this example\documentclass[a4paper,12pt]{article} \usepackage{mathtools} \begin{document} \[\int\limits_{\frac{1-\sqrt{2(-1+3y_2)}}{3}}^{1}\!\!\frac{1}{4\sqrt{R}}\] \end{document}– Sebastiano Apr 24 '19 at 18:35