Question

find the sum of the first 15 multiples of 8

Answer 1

We know that s = n/2(2a + (n-1)d)

                          = 15/2(2 * 8 + (15-1) * 8)

                          = 15/2(16 + 112)

                          = 15/2 * 128

                          = 15 * 64

                          = 960

Hope this helps!

Answer 2

Answer:

a = 8

n = 15

d = 8

So,Sn = n/2 [2a +(n-1)d)

= 15/2 (2×8 + (14)8]

= 15/2 [16 +112]

= 15/2 [128]

= 15 [64]

= 960