Question

2. Find the sum of the geometric series.

Answer 1

$\\ \rm\Rrightarrow \sum^{18}_{n=1}2n-1$

$\\ \rm\Rrightarrow 2(1)-1+2(2)-1\dots+2(18)-1$

• a=2-1=1
• a_18=l=36-1=35

So

$\\ \rm\Rrightarrow S_n=\dfrac{n(a+l)}{2}$

$\\ \rm\Rrightarrow S_n=\dfrac{18(1+35)}{2}=9(36)=324$

Answer 2

Answer:

324

Step-by-step explanation:

** The attachment shows an arithmetic sequence **

Sum of Arithmetic Series formula

$S_n=\dfrac12n(a+l)$

where:

• a = initial term
• l = last term

$a_n=2n-1$

$\implies a_1=2(1)-1=1$

$\implies a_{18}=2(18)-1=35$

$\implies S_{18}=\dfrac12(18)(1+35)=324$