Question 6829
A logarithm (log) of a number x is defined by the following equations. If

{{{x = 10^y}}}
then
 
log(x) = y.
Logarithms  relationships . For example, 

log(x) + log(y) = log(xy)
log(x) - log(y) = log(x/y)
log(1/x) = log(x-1) = -log(x)
log(xy) = y log(x) 
Logarithm rules

Log x (ab) = Logx  a  +  Log x  b
                            

Log x(a^b) = b Logx  a
      
{"Log" with a subscript of x}
Example:
What's the log to the base 5 of 625?  In 
other words, find the value of:

Log5 625.
  

Well, since 5^4 = 625, the log (to the base 5) of 625 is 4.