Maths

(x - √3)^2 + | y - cos 30 | = 0
Since (x - √3)^2 >= 0 and | y - cos 30 | >= 0
So (x - √3)^2 = 0 and | y - cos 30 | = 0 for their sum = 0
x = √3 and y = cos 30 = √3 /2
(3xy - x^2 y^2) / (xy - 1) * (1/xy - 1)
= (3xy - x^2 y^2) / (xy - 1) * (1 - xy)/xy
= (x^2 y^2 - 3xy) / xy
= xy - 3
= √3 * √3 /2 - 3
= 3/2 - 3
= - 3/2