Question 1100090
A logarithm is an exponent, and logarithms follow rules of exponents.


{{{b^x=y}}}
b, the base
x, the exponent, and later, called logarithm
y, result of raising base b, to power x.


Different notation:
{{{log(b,y)=x}}}



Not a very thorough explanation, but maybe your book will make more sense for you.


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The specific numerical example you asked about:
{{{0.000715*10^(-4)}}}
which you wanted completely as base of 10, raised to some power.

Using scientific notation, given numerical expression is
{{{(7.15*10^(-4))*10^(-4)}}}
{{{7.15*10^(-4)*10^(-4)}}}
{{{7.15*10^(-8)}}}
but you want ALL of the number as 10 raised to some power.


You use either table of logs or a calculator to find what is {{{10^n=7.15}}}.
The base is 10;
the logarithm is n;
the antilog is 7.15.
{{{n=log(10,7.15)}}}.   Do whatever you need on your calculator to find this n.  Mine  (on the computer) indicates {{{log(10,7.15)=0.854306}}};
If using Google, this tells me log(10,7.15)=0.854306;
(You probably want to near more than as 0.8543.)


So now your entire given number is {{{10^(0.8543)*10^(-8)=10^(-8+0.8543)=highlight(10^(-7.146))}}}.