Question

If the sum of first n terms of an A.P is Sn=5n square+3n then find out the 10th term of the A.P

Answer 1

Sn = 5n^2 +3n

=> n/2 [ 2a +(n-1) d] = n ( 5n +3)

=> 2a + (n-1) d = 2n/n ( 5n+3)

=> 2a + (n-1) d = 2(5n +3)

=> 2a + (n-1) d = 10n + 6

=> 2a +(n-1) d = 10n - 10 + 16

=> 2a +(n-1) d = 16 + 10(n-1)

On Comparing both sides, we get

a = 8

d = 10

T10 = a + 9d

= 8 + 90

= 98

Answer 2

Hi,

Please see the attached file!

Thanks