1. The problem statement, all variables and given/known data I'm taking a math of investment and credit course, in this case, solving for i which is the interest rate. My question is: is it possible to "ln both sides" of an equation? Like in (b) below, I know I could say y*ln(1+i) = ln(3). 2. Relevant equations (a) 5(1+i)^8 + 10(1+i)^4 = 3 (b) (1+i)^y = 3 3. The attempt at a solution I've already solved the actual question (a) by making the substitution x=(1+i)^4 and solving via quadratic equation. What I'm looking for is a more general method for solving these sort of questions. Something like "lning both sides": 40ln(1+i) + 40ln(1+i) = ln3 ln(ab) = ln(a) + ln(b) so I know that isn't correct. What is the correct form? Thanks in advance!