Question

an = 4n ²-1 . Find 8th term​

Answer 1

An = 4n²-1

=> A1 = 4-1 = 3 = a

=> A2 = 4(2)²-1 = 16-1 = 15

t2 = A2 - A1 = 15 - 3 = 12

d = t2 - a = 12 - 3 = 9

8th term = t8 = a +(n-1)d

=> t8 = 3 + (8-1) 9

=> t8 = 3+63 = 66

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Answer 2

$a_n = 4 {n }^{2} - 1 \\ a_1 = 4 \times {1}^{2} - 1 = 3 \\ a_2 = 4 \times {2}^{2} - 1 = 15 \\ 2 {}^{st} term = 15 - 3 = 12\\Common\: Difference=9\\{8}^{th}term={2}^{nd}term+6\times d\\ =12+6\times 9\\ =66$

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