因1/a+1/b=4,得4ab=a+b.a与b1/4且a0,b0.
由 (a-2ab-b)/(2a-2b+7ab),代入4ab=a+b,并简化,
得(2a-6b)/(15a-b).
由4ab=a+b,得a=b/(4b-1),代入上式,得
(6b-2)/(b-4) (b0,b4,b1/4)