A geometrical problem

There is a geometrical problem, how to draw an equi-lateral triangle in a three-parrel plane using an unscaled ruler and compass, each vertex placed on each parrel line respectively, as shown on the left.

Solution.
Assume x2>x1>0, so b>a
By calculation,
xo=3^.5*(a-b);
yo=(a+b).

So now it is straightforward to draw the triangle, noting that how to draw 3^0.5!