Question

please answer this question ​

Answer 1

Step-by-step explanation:

sum of 15 multiples of 8 is 960

for explanation see the attachment

Answer 2

$\sf{\bold{\green{\underline{\underline{Given}}}}}$

⠀⠀⠀⠀

• First term = a = 8
• common difference = d = 8
• No. of times = 15

______________________

$\sf{\bold{\green{\underline{\underline{To\:Find}}}}}$

⠀⠀⠀⠀

• Sum of first 15 terms = ??

______________________

$\sf{\bold{\green{\underline{\underline{Solution}}}}}$

⠀⠀⠀⠀

$\sf{\red{\boxed{\bold{S = \dfrac{n}{2} [ 2a + ( n - 1 ) d ] }}}}$

⠀⠀⠀⠀

$\sf : \implies\: {\bold{ S = \dfrac{15}{2} [ 2\times 8 + ( 15 - 1 ) 8 ] }}$

⠀⠀⠀⠀

$\sf : \implies\: {\bold{ S = \dfrac{15}{2} [ 2\times 8 + 14 \times 8] }}$

⠀⠀⠀⠀

$\sf : \implies\: {\bold{ S = \dfrac{15}{2} [ 16 + 14 \times 8] }}$

⠀⠀⠀⠀

$\sf : \implies\: {\bold{ S = \dfrac{15}{2} [ 16 + 112] }}$

⠀⠀⠀⠀

$\sf : \implies\: {\bold{ S = \dfrac{15}{2} \times 128 }}$

⠀⠀⠀⠀

$\sf : \implies\: {\bold{ S = 15 \times 64}}$

⠀⠀⠀⠀

$\sf : \implies\: {\bold{ S = 960 }}$

⠀⠀⠀⠀

⠀⠀⠀⠀

______________________

$\sf{\bold{\green{\underline{\underline{Answer}}}}}$

⠀⠀⠀⠀

• Sum of first 15 multiples of 8 is 960