Question

the sum of x term of an AP n2+3n find its 20th term

Answer 1

Here S

n

=3n+n

2

Now, first term a=S

1

⇒a=3×1+1

2

=4 and

Sum of first two terms=a

1

+a

2

=a+(a+d)=S

2

=3×2+2

2

=10

⇒2a+d=10⇒8+d=10⇒d=2

Now, a

2

=a+d⇒a

2

=4+2=6

a

3

=a+2d⇒a

3

=4+2×2=8

a

15

=a+14d⇒a

15

=4+14×2=32

Answer 2

Answer:

let suppose x

2+3 n2

20th