Find the ( 9^{text {th }} ) partial sum of the geometric sequence ( a_{n}=3^{n-1} ).

Question

Accepted Answer

Step:1 ：( S_{9} = frac{a_{1}(1 - r^{9})}{1 - r} )Step:2 ：( S_{9} = frac{3^{1 - 1}(1 - 3^{9 - 1})}{1 - 3} )Step:3 ：( S_{9} = -frac{3^{8} - 1}{2} )

Answer

Step: 1 ：( S_{9} = frac{a_{1}(1 - r^{9})}{1 - r} )Step: 2 ：( S_{9} = frac{3^{1 - 1}(1 - 3^{9 - 1})}{1 - 3} )Step: 3 ：( S_{9} = -frac{3^{8} - 1}{2} )

Find the \( 9^{\text {th }} \) partial sum of the geometric sequence \( a_{n}=3^{n-1} \).