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