This follows directly from change of base: $log_a$(b) = 1/$log_b$(a). Useful in simplifying products of logs with swapped bases. Extended: $log_a$(b)$log_b$(c)$log_c$(d) = $log_a$(d) (chain multiplication). Example: $log_2$(3)$log_3$(4)$log_4$(5)*$log_5$(2) = $log_2$(2) = 1.