Question 810762
<pre>  
   {{{drawing(200,200,-.2,1.2,-.2,1.2,

green(line(.5,sqrt(3)/2,.5,0)),locate(.53,.43,6),

locate(0,0,A), locate(1,0,B),locate(.48,.97,C),locate(.48,0,D),

triangle(0,0,1,0,.5,sqrt(3)/2) )}}}
        AB = AC

        AB = 2AD

      Area = {{{1/2}}}AB·CD = {{{1/2}}}AB·6 = 3AB = 3(2AD) = 6AD

      Area = 6AD

 ADČ + CDČ = ACČ = ABČ = (2AD)Č = 4ADČ

 ADČ + CDČ = 4ADČ

       CDČ = 3ADČ

        6Č = 3ADČ

        36 = 3ADČ
        
        12 = ADČ

       &#8730;<span style="text-decoration: overline">12</span> = AD

      &#8730;<span style="text-decoration: overline">4·3</span> = AD

       2&#8730;<span style="text-decoration: overline">3</span> = AD

Area = 6AD = 6(2&#8730;<span style="text-decoration: overline">3</span>) = 12&#8730;<span style="text-decoration: overline">3</span>

Edwin</pre>