Answer
First three terms: $2,8,14$
last term: $116$
Sum of the an arithmetic series: $1180$
Work Step by Step
First three terms can be found as:$a_1=6-4=2;a_2=12-4=8;a_3=18-4=14$
Last term can be found as: $a_{20}=6(20)-4=116$
Sum of the an arithmetic series can be calculated by using formula $S_n=\dfrac{n}{2}(a_1+a_n)$
Here $n=20$
Thus,
$S_{20}=\dfrac{20}{2}(2+116)=1180$
our results are:
First three terms: $2,8,14$
last term: $116$
Sum of the an arithmetic series: $1180$
