(√a+√(a-2))^2-(2√(a-1))^2
=[2a-2+2√a(a-2)]-(4a-4)
=2(√a(a-2)-(a-1))
(√a(a-2))^2-(a-1)^2
=(a^2-2a)-(a^2-2a+1)
=-1