Question

Find the sum of 16 terms of an ap -1,-5,-9

Answer 1

Answer:

Step-by-step explanation:

Here it is

Answer 2

$\red{\large {\underline{ \underline{ \star \: {Given:-}}}}}$

An A.P :- -1 , -5 , -9.

so,

a = -1 and d = -4.

$\red{\large {\underline{ \underline{ \star \: {Solution:-}}}}}$

$\sf S_n = \frac{n}{2} [ 2a + (n - 1)d]. \\ \\ \implies \frac{16}{2} \times 2( - 1) + 16 - 1 \times - 4. \\ \\ \implies 8 \times - 2 + 15( - 4). \\ \\ \implies - 16 + ( - 60). \\ \\ \implies - 76.$

$Sun \: of \: {16}^{th} terms.$

$\red{ \huge \implies {\underline {\underline{ - 76}}}}$

Formula Using :-

$\sf S_n = \frac{n}{2} [2a + (n - 1)d].$