Question

If sum of first n terms of an A.P is 2n2 + 7n, write its nth term.​

Answer 1

Step-by-step explanation:

Sn = 2n² + 7n

S1 = a1 = 2(1)² + 7(1) = 2 + 7 = 9

S2 = a1 + a2 = 2(2)² + 7(2) = 8 + 14 = 22

S3 = a1 + a2 + a3 = 2(3)² + 7(3) = 18 + 21 = 39

a1 = 9

a1 + a2 = 22;

9 + a2 = 22 ; a2 = 22 - 9 ; a2 = 13

a1 + a2 + a3 = 39

9 + 13 + a3 = 39 ; a3 = 39 - 22 = 17

a1 = 9 a2 = 13 a3 = 17

d = a2 - a1 = a3 - a2

13 - 9 = 17 - 13

4 =. 4

therefore common difference = d = 4

an = a + (n-1)d

an = 9 + (n - 1)(4)

an = 9 + 4n - 4

an = 5 + 4n

the nth term of the AP is --> 5 + 4n

Hope you get your answer

Answer 2

Answer:

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Step-by-step explanation:

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