The common logarithm of a number is the exponent you have to raise by, to get the desired number. For example,
In the similarity , you could just as easily replace the exponent with since this is equal to If a logarithm, is an exponent to , you can directly determine the power of ten value by reading of the logarithms argument,
Overall, this can be written in the following way.
You can only calculate logarithms of positive numbers. There's no number that you can raise 10 to in order to get zero or a negative result. As a result, this identity applies only when