ОН=[b]r[/b]=[m]\frac{a\sqrt{3}}{6}[/m]
[m]cos60 ° =\frac{OH}{SH}[/m]
[m]SH=\frac{OH}{cos60 ° }=\frac{a\sqrt{3}}{3}[/m]
S_(пп)=S_(осн)+S_(бок)=[m]\frac{a^2\sqrt{3}}{4}+3\cdot \frac{1}{2} a\cdot \frac{a\sqrt{3}}{3}=\frac{a^2\sqrt{3}}{4}+\frac{a^2\sqrt{3}}{2}=\frac{3a^2\sqrt{3}}{4}[/m]