#### Answer

$a_{5}=a_{1}\times r^{5-1}=a_{1}\times r^{4}=\left( -\dfrac {1}{8}\right) \times 4^{4}=-32;$
$a_{n}=a_{1}\times r^{n-1}=\left( -\dfrac {1}{8}\right) \times 4^{n-1}$

#### Work Step by Step

$a_{1}\times r^{2}=a_{3}\Rightarrow a_{1}=\dfrac {a_{3}}{r^{2}}=\dfrac {-2}{4^{2}}=-\dfrac {1}{8};a_{5}=a_{1}\times r^{5-1}=a_{1}\times r^{4}=\left( -\dfrac {1}{8}\right) \times 4^{4}=-32;a_{n}=a_{1}\times r^{n-1}=\left( -\dfrac {1}{8}\right) \times 4^{n-1}$