Answer:
Proved
Step-by-step explanation:
Given
[tex]a_n = 2n[/tex]
Required
Prove that [tex]S_n = n(n+1)[/tex]
The given sequence is an arithmetic sequence.
The Sn of this sequence is:
[tex]S_n = \frac{n}{2}(a_1 + a_n)[/tex]
Calculate a1
[tex]a_n =2n[/tex]
[tex]a_1 =2*1[/tex]
[tex]a_1 =2[/tex]
So, we have:
[tex]S_n = \frac{n}{2}(a_1 + a_n)[/tex]
[tex]S_n = \frac{n}{2}(2 + 2n)[/tex]
Factor out 2
[tex]S_n = \frac{n*2}{2}(1 + n)[/tex]
[tex]S_n = n(1 + n)[/tex]
[tex]S_n = n(n + 1)[/tex] --- Proved
