log a b = log b a
lgb/lga = lga/lgb
lg²b = lg²a
lg²b - lg²a = 0
(lgb + lga)(lgb - lga) = 0
lgb = lga 或 lgb = -lga = lg(1/a)
所以 b = a 或 b = 1/a
所以 a = b 或 a = 1/
log a b = log b a
lgb/lga = lga/lgb
lg²b = lg²a
lg²b - lg²a = 0
(lgb + lga)(lgb - lga) = 0
lgb = lga 或 lgb = -lga = lg(1/a)
所以 b = a 或 b = 1/a
所以 a = b 或 a = 1/