Exponent, to a negative exponent. Stroud problem.

Hi,

I'm a little confused with a problem (very!) early on in the 5th edition of Stroud's Engineering Mathematics.

F1 (pg. 69), #14c

Write each of the following as a number raised to a power: http://quicklatex.com/cache3/ql_6f64...6557e2e_l3.png

The answer given is: http://quicklatex.com/cache3/ql_35eb...bc4c108_l3.png

Naively, I thought:

http://quicklatex.com/cache3/ql_00e9...8fa729e_l3.png

http://quicklatex.com/cache3/ql_5881...9fa4134_l3.png

Although I guess http://quicklatex.com/cache3/ql_483d...d91a483_l3.png would be appropriate according to the wording of the question.

Clearly I'm missing something fundamental, can someone please point me in the right direction?