Question

The sum of n terms of an arithmetic sequence is 5n^2+2n
a.what is the sum of the first 2 terms of the sequence?
b. Write the first 2 terms of the sequence? ​

Answer 1

Step-by-step explanation:

here, Sn =5n^2+2n

a) let n be 2 then

A/Q,

Sn = 5x2^2+ 2x2

= 5 x 4 + 4

=24.. ..(i)... ans

b) (a+d) and (a-d) are two terms of ap

(a+d) + (a-d) = 24

a+a =24

2a = 24

a = 12... (ii)

since, 1st term +2nd term= 24

then 12+ 2nd term = 24

A2= 12

so, ap is 12,24 here d= 12