4a^2+4ab+b^2=0
(2a+b)^2=0
2a+b=0
b=-2a
a/b-b/a-(a^2+b^2)/ab
=a^2/ab-b^2/ab-(a^2+b^2)/ab
=(a^2-b^2)/ab-(a^2+b^2)/ab
=[(a^2-b^2)-(a^2+b^2)]/ab
=(a^2-b^2-a^2-b^2)/ab
=(-2b^2)/ab
=-2b/a
=-2*(-2a)/a
=4a/a
=4