>>697
|x|<1 のとき
log(1/(1-x)) = -log(1-x) = x+(x^2/2)+(x^3/3)+(x^4/4)+…
を使う

log(2) = log(1/(1-0.5)) = -log(1-0.5)
= 0.5+(0.5^2/2)+(0.5^3/3)+… = 0.69314…

-log(0.55) = -log(1-0.45)
= 0.45+(0.45^2/2)+(0.45^3/3)+… = 0.59783…

log[2](0.55) = -0.59783…/0.69314… = -0.86249…