Answer:
\(S_{20} =1680\).
Step-by-step explanation:
Given : 8 + 16 + 24 + 32 +…..
To find : Find S20
Solution : We have given 8 + 16 + 24 + 32 +…..
First term = 8.
Common difference = 16 - 8= 8
24 -16 = 8.
Sum of n term ( \(S_{n} =\frac{n}{2}[2 a+(n-1)d]\).
Where, a = first term , d =common difference .
For n = 20 , a = 8 , d = 8
\(S_{20} =\frac{20}{2}[2*8+(20-1) 8]\).
\(S_{20} =10[16+(19) 8]\).
\(S_{20} =10[16+152]\).
\(S_{20} =10[168]\).
\(S_{20} =1680\).
Therefore,4) \(S_{20} =1680\).
