Question

What is the sum of a 58–term arithmetic sequence where the first term is 6 and the last term is 405? please helpp.

Answer 1

The sum of an arythmetic sequence for first term, a1 and last term, an and up to the term, n is
$s_n= \frac{n(a1+an)}{2}$
n=58
a1=6
a58=405

$s_{58}= \frac{58(6+405)}{2}$
$s_{58}= \frac{58(411)}{2}$
$s_{58}= \frac{23838}{2}$
$s_{58}= 11919$


sum is 11,919