Question

If the sum of 1st term of an ap is 3n2-2n, find the common difference and its 20th terms

Answer 1

Given :

Sum of first term=3n²-2n

To find:

common difference d ,

20th term a20

Solⁿ:

Sum of first term = first term

so, 3n²-2n=a

3(1)²-2(1)=a

a=3-2=1

a=1

also, a2=3(2)²-2(2)

=12-4

=8

So, a2-a1=d

8-1=d

d =7

Now 20th term,a20=a+19d

=1+19(7)

=1+133=134

Thank You