Question 942020
Use 1 side as the hypotenuse and 1/2 of another side as the leg of a right triangle.
The other leg of that triangle will be the height. 
Using the Pythagorean theorem,
{{{12^2=(12/2)^2+H^2}}}
{{{H^2=144-36}}}
{{{H^2=108}}}
{{{H=6sqrt(3)}}} or formulaically, {{{H=(sqrt(3)/2)*S}}}