Answer:
Explained below.
Step-by-step explanation:
Consider the series is a set of first 6 natural numbers.
Sum of first n terms is:
[tex]\text{Sum of n terms}=\frac{n(n+1)}{2}[/tex]
[tex]\text{Sum of first 6 terms}=\frac{6(6+1)}{2}[/tex]
[tex]=3\times7\\=21[/tex]
Consider the series is an arithmetic sequence.
Sum of first n terms is:
[tex]S_{n}=\frac{n}{2} [2a+(n-1)d][/tex]
Here,
a = first term
d = common difference
Consider the series is an geometric sequence.
Sum of first n terms is:
[tex]S_{n}=\frac{a_{1}\cdot(1-r^{n})}{(1-r)}[/tex]
Here,
a₁ = first term
r = common ratio
