a) a_{n}= \frac{1}{2^{n-1}}an=12n1

S_{n}=1+\frac{1}{2}+\frac{1}{2^{2}}+...+\frac{1}{2^{n-1}} = \frac{1}{1-\frac{1}{2}}=2Sn=1+12+122+...+12n1=1112=2

b) p_{n}=4.\frac{1}{\left (\sqrt{2}  \right )^{n-1}}pn=4.1(2)n1