Negative Exponents
Taking a number to a negative exponent does not necessarily yield a
negative answer. Taking a base number to a negative exponent is equivalent
to taking the base number to the positive
opposite of the exponent
(the exponent
with the negative sign removed) and placing the result in the denominator of a
fraction whose numerator is 1. For example, 5^{4} = 1/5^{4} = 1/625.
6^{3} = 1/6^{3} = 1/216, and ( 3)^{2} = 1/( 3)^{2} = 1/9.
If the base number is a fraction, then the negative exponent switches the numerator and the denominator.
For example, (2/3)^{4} = (3/2)^{4} = (3^{4})/(2^{4}) = 81/16 and ( 5/6)^{3} = (6/( 5))^{3} = (6^{3})/(( 5)^{3}) = 216/( 125) =  216/125.
Negative Exponents and the Base Ten System
Here is a list of negative powers of ten:
10^{1}  =  1/10^{1} = 1/10 = 0.1 

10^{2}  =  1/10^{2} = 1/100 = 0.01 

10^{3}  =  1/10^{3} = 1/1, 000 = 0.001 

10^{4}  =  1/10^{4} = 1/10, 000 = 0.0001 

10^{5}  =  1/10^{5} = 1/100, 000 = 0.00001 

and so on...
Just as 10^{2} represents a 1 in the hundreds place,
10^{2} represents a 1 in the hundredths place. The
singledigit number in the hundredths place is the number that
is multiplied by 10^{2}.
Now we can write out any terminating
decimal as a sum of single
digit numbers times powers of ten. The number 23.45 has a 2 in the tens place
(2×10^{1}), a 3 in the ones place (3×10^{0}), a 4 in the tenths
place (4×10^{1}) and a 5 in the hundredths place (5×10^{2}).
Thus, 23.45 = 2×10^{1} +3×10^{0} +4×10^{1} +5×10^{2}.
Examples: Write out the following numbers as singledigit numbers times
powers of ten:
523.81 = 5×10^{2} +2×10^{1} +3×10^{0} +8×10^{1} +1×10^{2}
3.072 = 3×10^{0} +0×10^{1} +7×10^{2} +2×10^{3}
46.904 = 4×10^{1} +6×10^{0} +9×10^{1} +0×10^{2} +4×10^{3}