a^2b^2=1ab=±11/a+1/b=2(a+b)/ab=2a+b=2aba^2+b^2=(a+b)^2-2ab=(2ab)^2-2ab=4a^2b^2-2ab=4-2ab(a+b)/(a^2+b^2)=2ab/(4-2ab)=ab/(2-ab)当ab=1时ab/(2-ab)=1/(2-1)=1当ab=-1时ab/(2-ab)=-1/[2-(-1)]=-1/3所以(a+b)/(a...