Question

find S15 if for an A.P a=10 and d= 3​

Answer 1

Answer:

a = 10

d = 3

n = 15

$S_{n}= \frac{n}{2}(2a+(n-1)d)$

$S_{15}= \frac{15}{2}(2*10+(15-1)*3)$

$S_{15}= \frac{15}{2}(2*10+14*3)$

$S_{15}= \frac{15}{2}(20+42)$

$S_{15}= \frac{15}{2}(62)$

$S_{15}=15*31$

$S_{15}= 465$

Answer 2

Answer:

Refer to the image for step by step solution.

Hope it helps.