[tex]Se ~da: \\ \text{un triunghi echilateral cu latura } l.\\Se~cere: \\ h = inaltimea ~triunghiului. \\ Rezolvare: \\ h = \sqrt{l^2- (\frac{l}{2})^2 }=
\sqrt{l^2- \frac{l^2}{4}} = \sqrt{\frac{4l^2}{4}-\frac{l^2}{4}} =\sqrt{\frac{3l^2}{4}}=\boxed{ \frac{l \sqrt{3} }{2} }[/tex]
