S△OAB=ab/2=√3 c²
a²b²=12(c²)²
a²(a²-c²)=(a²)²-a²c²=12(c²)²
1-c²/a²=12(c²/a²)²
12(e²)²+e²-1=0
e²=1/4
e=1/2