Hello,
\(u_{1} =4\\
u_{2} =4*q\\
u_{3} =4*q^2\\
...\\
u_{9} =4*q^8\\\\
==\textgreater\ 4*q^8=1024\\
==\textgreater\ q^8=256\\
==\textgreater\ q=2\mbox{( and there is a problem in the question) } \ or \ q=-2\\
if\ q=2 \ then\ \sum_{i=0}^{8}\ 4*(2)^i= 4*\dfrac{1-2^9}{1-2} =2044\\
if \ q=-2 \ then\ \sum_{i=0}^{8}\ 4*(-2)^i= 4*\dfrac{1-(-2)^9}{1+2} =684\\\)
Answer B (but see the problem)
