# Definition of Common Logarithm

## Reference > Algebra: Common Logarithms

 DescriptionThe Definition of Common Logarithm Rule states that:$${b}^{a}=x$$ if and only if $$log_b(x)=a$$
 Examples${3}^{y}=7$1 Use Definition of Common Logarithm: $${b}^{a}=x$$ if and only if $$log_b(x)=a$$.$y=\log_{3}{7}$2 Use Change of Base Rule: $$\log_{b}{x}=\frac{\log_{a}{x}}{\log_{a}{b}}$$.$y=\frac{\log{7}}{\log{3}}$DoneDecimal Form: 1.771244y=log(7)/log(3)