Let point E be EF⊥x axis be at point F, and let point E (a,-a? -2a+3)(-3 & lt； a & lt0 )

∴EF=- a？ -2a+3，BF=a+3，OF=-a

∴S quadrilateral BOCE = BF? EF + (OC +EF)？ Belonging to

= 1/2( a+3)？ (-a？ -2a+3) + (- a？ -2a+6)？ (-a)

= -3/2( a+3/2)？ +63/8

∴ When a =-3/2, the BOCE of the s- quadrangle is the largest, and the maximum value is 63/8.

At this time, the coordinates of point E are (-3/2, 63/8).