Question

answer the above question​

Answer 1

Sk =

$\frac{1}{2}( 3 {k}^{2} + 7k)$

S1 =

$\frac{1}{2} (3 + 7)$

= 5

S2=

$\frac{1}{2} (12 + 14)$

= 13

S1 = a1

S2 = a1 + a2

So, a2 = S2 - S1

a2 = 8

=> 5 + (2-1)d =8

d = 3

Ak = a + (n -1)d

Ak = 5 + (n -1)3

Ak = 2 + 3n

20th term = a + 19 d

a20 = 5 + 57

a20 = 62

Therefore, kth term is 2 + 3n and a20 is 62..

Hope it helps you!!!