Question

the sum of the first 15 multiples of 8 is​

Answer 1

Answer:

8*1= 8

8*2=16

8*3=24

8*4=32

8*5=40

8*6=48

8*7=56

8*8=64

8*9=72

8*10=80

8*11=88

8*12=96

8*13=104

8*14=112

8*15=120

Answer 2

Step-by-step explanation:

The first 8 multiples of 8 are

8, 16, 24, 32, 40, 48, 56,64

These are in an A.P., having first term as 8 and common difference as 8.

Therefore, a = 8

d = 8

S15 = ?

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

S15 = 15/2 [2(8) + (15 - 1)8]

= 15/2[6 + (14) (8)]

= 15/2[16 + 112]

= 15(128)/2

= 15 × 64

= 960