Any straight line parallel to an asymptote of a hyperbola intersects the hyperbola at
Consider the hyperbola xy = 4 and a line 2x + y = 4. O is the centre of the hyperbola. Tangent at any point P on the hyperbola intersects the coordinate axes at A and B.
Let the given line intersect x-axis at R. If a line through R intersects the hyperbola at S and T, then the minimum value of (RS) (RT) is ___