1題中3數學題!唔識做!help!

Is ABCD a square?

2008-05-26 17:18:50 補充：
if yes,

2x-1 = 2y +1
i.e., x-y=1 ---- *

and
(2x-1)^2 + (2y+1)^2 = ( 開方18)^2
s.t.., 4x^2 - 4x + 4y^2 + 4y + 2 =18
i.e., x^2 - x + y^2 + y = 4 ---- **

sub * into **: (y+1)^2 - (y+1) + y^2 + y =4
y^2 + y - 2 = 0
y= 1 or y= -2(rejected)
so, x= 2
Thus, x=2 and y=1

ABCD is a a square