# Math Help - Help finding closed form of sum

1. ## Help finding closed form of sum

Hello all. Can somebody please help with the intermediate steps here? I have reached the point given, but not sure how to advance to the final solution. Many thanks

$\sum_{i=0}^9 (1/2z)^{n}=\frac{1-(2z)^{-10}}{1-(2z)^{-1}}$

2. that's all, that's a closed form.

don't know what you want to do further.

3. Sorry, I wanted to know the necessary steps I need to take to get it into the closed form, the first equation is where I got to, I have the solution but don't know how to get there :-)

4. ah okay then, can you prove that $\sum_{j=0}^n a^j=\frac{a^{n+1}-1}{a-1}$ ?

if you can do that, then you're done. (This is a fact known as geometric sum.)

5. Many thanks, solved.