Question

The sum of first $n$ terms of an arithmetic sequence is $5n^2+2n$.
(a) What is the sum of first two terms of this sequence?
(b) Write the first two terms of the sequence.

Answer 1

$a_n=5n^2+2n$
(a) First term $=5(1{)}^2+2(1)=5+2=7$
Sum of the first two terms $=5(2{)}^2+2(2)=20+4=24$.
(b) First term $=7$
Second term $=24-7=17$.