Properties of the logarithm: for any base of logarithm,
log(a*b) = log(a) + log(b)
If we replace b with 1/b, or b^-1, we have
log(a/b) = log(a) + log(1/b) = log(a) - log(b)
since
log(1/b) = log(b^-1) = - log(b)
using the power property of logarithms,
log(b^n) = n log(b)
Now,
ln35 = ln(5*7) = ln5 + ln7
ln(1/7) = - ln7
ln25 = ln(5^2) = 2 ln5
Putting everything together, we have
(ln35 + ln(1/7))/ln25 = (ln5 + ln7 - ln7)/(2 ln5) = ln5/(2 ln5) = 1/2
