Question

The sum of n term of an

a.P . Is n2+3n find its 20th term

Answer 1

Answer:

sn=n²+3n

n/2[2a+(n-1)d]=n²+3n

2an+(n²-n)d=2n²+6n

n{2a+(n-1)d}=n(2n+6)

2a+(n-1)d=2n+6

d=2n+6-2a/n-1

20th term=a+19d

a+19.(2n+6-2a)/n-1

na-a+38n+114-18a/n-1

na-19a+38n+114/n-1

match the answer if not match then tell me.i am trying to solve it again