5. (Zhejiang Jinhua, 2007) As shown in figure 1, hyperbola is known.

y = xk(k & gt； 0) The straight line y = k ′ x intersects at points A and B, and point A is in the first quadrant. Try to solve the following problem: (1) If the coordinate of point A is (4,2) and the coordinate of point B is.

; If the abscissa of point A is m, the coordinates of point B can be expressed as

; (2) As shown in Figure 2, cross the origin O and make another straight line L, which intersects the hyperbola.

y = xk(k & gt； 0) at p and q, point p is in the first quadrant. ① indicates that the quadrilateral APBQ must be a parallelogram; ② the abscissas of points a and p are m and n, respectively. Can quadrilateral APBQ be a rectangle? Will it be a square? If possible, directly write out the conditions that mn should meet; If not, please explain why.