AB=x, AC=2√3 x
BC^2 =AB^2 +AC^2 -2 AB*AC cosA (теорема косинусов) =>
28 =x^2 +12x^2 -2* x *2√3 x *√3/2 => 28 =7x^2 => x=2
AB=2, AC=4√3
