Question

Find the sum of the first 15 multiples of 8.

Answer 1

Hello,

Question;-

Find the sum of the first 15 multiplies of 8

Method of Solution;-


Let to be a is first term and 'd'" is common Difference and l is last term of Given Arithmetic Sequence or Progression;-

Arithmetic Sequence or Progression which are given below;-

Arithmetic Sequence or Progression;-

8,16,24,32....

Here,

First term= 8

CommOn Difference=8

Number of terms=15

We know that Formula of Summation of Arithmetic Sequence or Progression.

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

S15=15/2(2x8+(15-1)8

  =15/2(16+(14)8)

  =15/2(16+112)

  =15/2 x 128

  =15 x 64

 =960


Hence ,960 are sum of the first 15 multiples of 8.

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