2(a+√3)(a-√3)-a(a-6)+6
=2(a^2-3)-a^2+6a+6
=2a^2-6-a^2+6a+6
=a^2+6a
=a(a+6)
当a=√2 -1时,a(a+6)=(√2 -1)(√2 -1+6)=4√2-3