Question

the sum of n terms of an AP is 7n2+3n.Find its 8th term​

Answer 1

Step-by-step explanation:

explanation in picture

Answer 2

Answer:

The 8th term of given AP is 108

Step-by-step explanation:

Given that,the sum of n terms of A.P is

$S _{n} = 7n {}^{2} + 3n$

Let the first term be a.We know that,Sum of 1st term is equal to first term.Therefore

$a = S _{1} = 7(1) {}^{2} + 3(1) = 10$

The sum of first two terms is given as follows

$S _{2} = (a) + (a + d) = 2a + d = 20 + d$

We know that,

$S _{2} = 7(2) {}^{2} + 3(2) = 34 \\ = > 34 = 20 + d = > d = 14$

Since,a and d are known,we can find the 8th term as follows

$t _{8} = a + (8 - 1)d = 10 + 7(14) = 108$

Therefore the 8th term of given AP is 108

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