(a+b)^2+(a-b)^2+(-2a+b)(a+b)=a^2+b^2+2ab+a^2+b^2-2ab-2a^2-2ab+ab+b^2=3b^2-ab
=b(3b-a)
(a^-1+b^-1)/(a^-1-b^-1)=(a+b)/(a-b)