Question

Second term in an AP is 8 & the 8th term is 2 more than the thrice the second term. Find the sum of first 8 terms​

Answer 1

a2 = 8....................... (1)

a+d = 8.................... (2)

= a8 =3( a2 )+2

a8 = 3×8+2 (using (1))

a8 = 26

a+7d = 26............. (3)

solving (2) & (3)

we get,

6d = 18

d = 3

put d = 3 in (1)

we get,

a = 5

S8 = n/2 (2a+(n-1)d)

= 8/2 (2×5+(8-1)3

= 4 (10+7×3)

= 4× 31

= 124

Answer 2

Given:

Second term in an AP is 8 & the 8th term is 2 more than the thrice the second term.

To Find:

Find the sum of first 8 terms​.

Solutions:

a2 = 8....................... (1)

a+d = 8.................... (2)

a8 =3(a2)+2

a8 = 3×8 + 2 (using (1))

a8 = 26

a+7d = 26............. (3)

solving (2) & (3), we get

6d = 18

  d = 3

put d = 3 in (1), we get

a = 5

S8 = n/2 (2a+(n-1)d)

     = 8/2 (2×5+(8-1)3

     = 4 (10+7×3)

     = 4× 31

     = 124

Hence, the sum of first 8 terms​ is 124.