Question 186906
{{{(7 * 10^3)*(8 * 10^-9)}}}
This are 4 different factors, and they can be
placed in any order without changing the 
expression
{{{7*8*10^3*10^-9}}}
{{{56*10^3*10^-9}}}
The general rule for negative exponents is:
{{{a^(-b) = 1/(a^b)}}}
another rule is:
{{{a^b*a^(-c) = a^(b-c)}}}
In this problem:
{{{10^-9 = 1/1000000000}}}
{{{10^3 = 1000}}}
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{{{10^3*10^-9 = 1000 * (1/1000000000)}}}
{{{1000 * (1/1000000000) = 1/1000000}}}
{{{1/1000000 = 10^-6}}}, so you see that
{{{10^3*10^-9 = 10^(3-9)}}}
{{{10^(3-9) = 10^-6}}}
So, the whole answer is
{{{56*10^-6}}}