In the isosceles trapezoid ABCD, ABDC, AB=, DC=, height CE=, diagonal AC and BD intersect H, and two straight lines MN and RQ parallel to the line segment BD move at the same time at a constant speed from point A to point C in the AC direction, intersecting the sides of the isosceles trapezoid ABCD at m, n, r and q respectively, and intersecting diagonal AC at f and g respectively; When the straight line RQ reaches the point C, the two straight lines stop moving at the same time. Remember that the graphic area of isosceles trapezoid ABCD swept by line MN is S 1, and the graphic area swept by line RQ is S2. If the translation speed of the straight line MN is 1 unit/second, the translation speed of the straight line RQ is 2 units/second, and the moving time of the two straight lines is x seconds.

(1) Fill in the blank: ∠ AHB = 90; AC = 4；

(2) If S2=3S 1, find x;

(3) let S2=mS 1, and find the variation range of m.fghd