Ответ:
0\ \ \to \ \ \boxed {\ sina=\dfrac{1}{5}\ }" alt="cosa=\dfrac{2\sqrt6}{5}\\\\\\sin^2a=1-cos^2a=1-\dfrac{4\cdot 6}{25}=\dfrac{1}{25}\ \ \ \Rightarrow \ \ \ sina=\pm \dfrac{1}{5}\\\\\\a\in \Big(\, 0\, ;\, \dfrac{\pi}{2}\, \Big)\ \ \ \Rightarrow \ \ \ sina>0\ \ \to \ \ \boxed {\ sina=\dfrac{1}{5}\ }" align="absmiddle" class="latex-formula">