From Förberedande kurs i matematik 1

By writing the argument \displaystyle 8 as \displaystyle 8 = 2\cdot 4 = 2\cdot 2\cdot 2 = 2^3, the logarithm law, \displaystyle \lg a^b = b\lg a, gives

\displaystyle \log _{2}8 = \log _{2} 2^3 = 3\cdot\log _{2}2 = 3\cdot 1 = 3\,,

where we have used \displaystyle \log _{2}2 = 1\,.