Question

The sum of first n terms of an A.P.is n/2(3n+13) find the 30th term

Answer 1

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Answer 2

Sn =n/2{3n +13 }

we know,

from sum of n terms formula,

Sn =n/2{ 2a + ( n -1)d}

we convert given An in standard formula,

Sn =n/2{ 2.(8) + ( n - 1)(3) }

= n/2{ 2.8 + ( n - 1)3}

now, you compare both Expression,

a = 8

d = 3

now ,
use formula,

Tn = a + (n - 1)d

T30 = 8 + ( 30 -1)(3)
=8 +29 x 3
=8 +87
=95