2log(a - 2b) = log(a) + log(b)
Using properties of logs:
---> log(a - 2b)2 = log(a·b)
---> (a - 2b)2 = ab
---> a2 - 4ab + 4b2 = ab
---> a2 - 5ab + 4b2 = 0
---> (a - 4b)(a - b) = 0
Either a - 4b = 0 ---> a = 4b ---> a/b = 4
or a - b = 0 ---> a = b [but this is impossible for it would make a - 2b negative]