![\operatorname{\log}_a5.8=7]()
1) Note that since we cannot reduce both sides of that equality to the same base, one way to rewrite it is to resort to a logarithm.
The Definition of a Logarithm is:

2) Now, we can rewrite that exponential statement as a logarithm that way:

Note that whenever the base of a logarithm is the same as the exponent of its argument we can tell that log is equal to its exponent.