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Change of base for logarithms

log⁡ab=log⁡cblog⁡ca\log_a b=\dfrac{\log_c b}{\log_c a}
For a,b,c>0a,b,c>0, a≠1a\neq1, c≠1c\neq1: log⁡ab=log⁡cblog⁡ca\log_a b=\dfrac{\log_c b}{\log_c a}. Often c=10c=10 (lg⁡\lg) or c=ec=e (ln⁡\ln). Consequence: log⁡ab⋅log⁡ba=1\log_a b\cdot\log_b a=1 when b≠1b\neq1.
Denominator log⁡ca≠0\log_c a\neq0
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