|a-2|+b²-2b+1=0
(a-2)+(b-1)^2=0
(a-2)=0,a=2
(b-1)^2=0,b=1
-a²-9b²+6ab
=-(a²-6ab+9b²)
=-(a-3b)^2
=-(2-3)
=1