Question

The sum of n terms of an AP is 2n2+n. Then 8th term of the AP is
(A) 27
(B) 31
(C) 35
(D) 39​

Answer 1

Step-by-step explanation:

so option is b

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Answer 2

Step-by-step explanation:

$\huge\bf{\mid{\overline{\underline{ANSWER:-}}\mid}}$

$\huge\bold{GIVEN:-} \\ \\ S_n \: of \: A. P \: is \: 2{n}^{2} + n. \\ \\ \huge\bold{ To \: find:-} \\ \\ t_8 = ?$

$If \: we \: put \: \boxed{ \red{n = 8 }} \implies \\ \\ S_8 = 2 {8}^{2} + 8 \\ \\ \implies 128 + 8 \\ \\ \implies 136 \\ \\ S_7 = 2 {7}^{2} + 7 \\ \\ \implies 98 + 7 \\ \\ \implies 105 \\ \\ Now, \: \blue{S_8 - S_7 } \: will \: give \: you \: t_8 ... \\ \\ S_8 - S_7 \\ \\ \implies 136 - 105 \\ \\ \huge{\boxed{\boxed{ \implies 31 }}}$

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