Question

Find the sum of the first 15 multiples of 8?

Answer 1

AP----- 8,16,24,32,..........

a=8 common difference d=8

no.of terms = 15

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

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

= 15 /2 (16+112)

= (15* 128 ) / 2

=15*64

= 960

Answer 2

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.