|a-1|+(b+1)^2=0
a=1 b=-1
[ (2a+b)^2-(2a+b)(2a-b)-6b ]/2b
=[4a^2+4ab+b^2-4a^2+b^2-6b]/2b
=[2b^2+4ab-6b]/2b
=b+2a-3
=-1+2-3=-2