Calculate logarithms.
log_b(x) = y means b^y = x; the common log uses base 10 and the natural log uses base e.
log10(1000) = 3; ln(e²) = 2.
log usually means base 10 (common log), while ln is the natural log with base e ≈ 2.718.
Yes. Use the change-of-base formula: log_b(x) = ln(x) / ln(b).
Logarithms of zero or negative numbers are undefined in the real numbers.