Question

Find the series whose sum to n terms is 5n²+3n.

Answer 1

First term= Sum of first 1 term= 5+3= 8

Second term= Sum of 2 terms- t1= 20+6-8= 18

Third term= Sum of 3 terms-T1-T2=45+9-18-8= 28

Thus, we conclude that the series is an AP with first term=8 and common difference= 18-8=28-18=10

Thus, required series= 8,18,28,38,48,58,68,78,...............

Answer 2

HERE IS YOUR ANSWER

Let n=1,we have

5n^2+3n

5(1)^2+3(1)

5×1+3

5+3

=8

Let n=2,we have

5(2)^2+3(2)

5(4)+3(2)

20+6

=26

Let n=3,we have

5(3)^2+3(3)

5(9)+9

45+9

=54

a=8

d=26-8

=18

THE SERIES IS:-

8,26,54,72,90.......

THANK YOU

HOPE IT HELPS YOU