heh, come to think of it, so is the first one:

it is given that log((a-b)/4) = log sqrta + log sqrtb, thus (a-b)/4 = sqrt(ab), thus, ((a-b)/4)^2 = ab, thus, (a-b)^2 = 16ab, thus a^2 - 2ab + b^2 = 16ab. Adding 4ab to both sides, a^2 + 2ab + b^2 = 20 ab, giving (a+b)^2 = 20ab.