>>61の間違った解き方

(1 + x)^n = 1 + n・x

log_(1 + x) (1 + x)^n = log_(1 + x) (1 + n・x)

n = log_(1 + x) n・(1/n + x)

n = n・log_(1 + x) (1/n + x)

log_(1 + x) (1/n + x) = 1

1/n + x = 1 + x

n = 1