Formula to find the sum of nth terms of an arithmetic sequence is:
[tex] S_{n} =\frac{n}{2} (a_{1} +a_{n}) [/tex]
Where, [tex] S_{n} [/tex] = sum of nth terms.
[tex] a_{1} [/tex] = first term.
[tex] a_{n} [/tex] = last term.
Now we need to find, sum of a 58th arithmetic sequence where the first term is 6 and the last term is 405 .
So, plug in n = 58, [tex] a_{1} [/tex] = 6 and [tex] a_{n} [/tex] = 405 in the above formula.
[tex] S_{58} =\frac{58}{2} (6+405) [/tex]
= [tex] \frac{58}{2} (411) [/tex]
=[tex] \frac{23838}{2} [/tex]
= 11919
So, the sum of 58th terms is 11919.
Hope this helps you!.
